Full text of "The Moon in Modern Astronomy: Summary of Twenty Years Selenographic Work ..."

See other formats

This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project
to make the world's books discoverable online.

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the
publisher to a library and finally to you.

Usage guidelines

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.

We also ask that you:

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.

+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.

+ Maintain attribution The Google "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liability can be quite severe.

About Google Book Search

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web

at jhttp : //books . qooqle . com/

IE MOON

"ODERN ASTRONOMY
BY Pi 7H

TITH AN INTRODUCTION
BY

J. E. GORE. F.R.A.S.

i |H||pi|l|

'■''■'..'. ■|i!i !; l|.

THE MOON

MODERN ASTRONOMY

SUMMARY OF TWENTY YEARS SELENOGRAPHIC WORK, AND
A STUDY OF RECENT PROBLEMS

PHILIP FAUTH

With 66 Illustrations and a Frontispiece

Translated by Joseph McCabe, with an
Introduction by

J. ELLARD GORE

F.R.A.S., M.R.I.A., Etc.

D. VAN NOSTRAND COMPANY

23 MURRAY AND 27 WARREN STREETS,

NEW YORK
1909

ASTRONOMY
LIBRARY

:rr

CONTENTS

Page

Introduction ... ... ... ... ... ... ... 7

1. Maria ... ... ... ... ... ... ... 9

. 2. Mountain Chains and Ridges ... ... ... 9

3. Crater Mountains, Walled and Ring Plains ... 11

4. Valleys and Clefts or Rills ... ... ... 12

Author's Preface ... ... ... ... ... ... 19

Chapter I. Historical Survey ... ... ... ... 23

IF. Appearance and Reality ... ... ... 59

III. Light and Colour ... ... ... ... 78

IV. The Ring Mountains ... ... .. ... 98

V. The Remaining Elevations and Rills ... 122

VI. Some Conclusions ... ... ... ... 135

260022

INTRODUCTION

The moon being the nearest celestial body to the
earth naturally forms an object of especial interest.
Its mean distance from the earth is about 238,840
miles, but, owing to the elliptical shape of its orbit,
this distance is sometimes increased to nearly 253,000,
and sometimes diminished to about 221,600 miles.
The mean period of revolution round the earth is
27 days, 7 hours, 43 minutes, 11 \ seconds, and as it
rotates on its axis in the same time that it revolves
round the earth, this is also the length of its day. Its
diameter is about 2160 miles, so that in volume the
earth is about 49J times larger. In mass, however,
the earth is about 81 times greater, and hence the
moon's density is equal to 49 \ divided by 81, or about
0*608 that of the earth, or taking the earth's density
as 5 '53, that of the moon is 3*36 (water equal unity).
From the above data it follows that the force of gravity
at the moon's surface is about one-sixth of terrestrial
gravity. If, therefore, a man of 12 stone weight were
transferred to the moon he would weigh only 2 stone,
so that a much larger race of men than ourselves
would be theoretically possible on the moon. As,
however, the moon has neither air nor water, the
existence of any form of life on its surface seems more

• • • • • • „«

• • •• • •/ •

8.-. ::•:••• ••• introduction

than doubtful. The moon's surface is about equal
in area to North and South America, but as we only-
see one side of it — owing to its period of axial rotation
being equal to that of its revolution round the earth —
the surface we see may be stated as roughly equal to
that of North America.

Examined with the naked eye or an opera glass
the moon's surface is seen to be chequered with bright
and dusky patches. Near the southern edge of the
disc is a luminous spot known as Tycho, an immense
4 crater ring,' which has been well termed by Webb
* the metropolitan crater of the moon.' Near the
northern limb, is a darkish spot known as Plato. In
the north-east quadrant, not far from the moon's
visible centre is the magnificent crater Copernicus.
Near the centre is another fine walled plain called
Albategnius, and between the centre and Plato a
very regular one known as Archimedes. The most
brilliant spot on the moon's surface is the ' crater '
Aristarchus, near the north-eastern edge. The dark
portions, formerly termed Maria, under the mistaken
idea that they represented lunar seas, cover a consider-
able area of the moon's surface, and are conspicuously
visible even to the naked eye. Two of these remarkable
spots are seen near the northern edge. Of these the
western one is known as the Mare Serenitatis or Sea
of Serenity, and the eastern the Mare Imbrium or
Sea of Clouds. To the south of the Mare Serenitatis
is another large patch called the Mare Tranquillitatis ;
and to the west of this, and near the edge of the disc,
is. a conspicuous spot known as the Mare Crisium.
Near the eastern edge is another well-marked spot

INTRODUCTION 9

called the Oceanus Procellarum, and there are other
dark markings in the south-eastern portion of the
disc.

The most remarkable features of the moon's
surface may be divided into : 1. — Maria or Seas;
2. — Mountain Chains ; 3. — * Crater ' Mountains, Walled
and Ringed Plains ; and 4. — Valleys and Clefts or
' Rills.'

1. Maria. — The most conspicuous of these have
been already referred to. They are comparatively
level surfaces and are known not to be seas from the
fact that where the moon's c terminator ' (or bounding
line between light and darkness) crosses them it has
a broken and irregular outline, whereas the edge of
the shadow would form a regular curve if it crossed
a water surface. These so-called * seas ' are, however,
not quite level, as they include many small hills and
pits, but they may be considered as flat when compared
with the other parts of the moon's surface which are
exceedingly rugged and irregular.

.- 2. Mountain Chains and Ridges. — These are
somewhat similar in their general outlines to the
mountains of the earth, but are comparatively much
higher. The most conspicuous of these mountain
ranges is that known as the Apennines, which runs
from Copernicus to the Mare Serenitatis, a distance of
about 460 miles. They are. of considerable elevation
with peaks ranging from 11,000 to about 20,000 feet in

10 INTRODtJCTIOK

height. Near Plato there is a lofty range called the
Alps, and to one of its summits, about 12,000 feet in
height, Schroter gave the name of Mont Blanc. Cutting
across this chain of mountains is a marvellous valley
nearly 100 miles long and several miles wide, in which
our terrestrial Mont Perdu would be literally lost !
In the south-western quadrant there is a long range
known as the Altai mountains, about 280 miles in
length and attaining an altitude of about 13,000 feet.
At its southern extremity there is a fine ' crater ' ring
called Piccolomini, a circle about 57 miles in diameter,
on the eastern edge of which is a peak about the
height of our Mont Blanc.

On the extreme southern edge of the disc is a
wonderful range known as the Leibnitz Mountains.
Several peaks reach a height of nearly 30,000 feet,
and to one of them Neville (Neison) assigns an altitude
of nearly 36,000 feet, or 7,000 feet higher than Mount
Everest, the highest of the Himalayas ! Under
favourable conditions these giant mountains are
actually visible in profile on the moon's limb. The
same remark applies to the Doerf ul Mountains situated
near the Leibnitz range on the south-east limb, the
highest of which was estimated by Schroter at 25,000
or 26,000 feet. As the sun never sets on the Leibnitz
and Doerf ul Mountains, Flammarion calls them c the
mountains of eternal light.' Along the eastern limb
are ranges called the Cordilleras, and the D'Alembert
and Rook Mountains which reach a height of nearly
20,000 feet. Another lofty mass is the Caucasus,
north-east of Archimedes, with peaks rising to 18,000
Or 19,000 feet. Some of the ' ridges ' are narrow

INTRODUCTION 11

backs of small height but of great length. One of
these runs for a length of over 600 miles, apparently
connecting Copernicus with a small 'crater' called
Kirch (between Archimedes and Plato).

3. Crater Mountains, Walled and Ring Plains.—
The so-called * craters ' are, perhaps, the most remark-
able and interesting features of the moon's surface.
They are usually supposed to be of volcanic origin,
but their enormous size seems opposed to this hypo-
thesis. Of these curious objects Tycho, already
referred to, is a perfect specimen. It has a diameter
of over 50 miles, with a depth of nearly 17,000 feet,
and a central hill of about 6,000 feet in height. The
diameter of Copernicus is about 56 miles, with a peak
on its ring rising to a height of about 11,000 feet
above the floor of the 'crater' and several central
hills. Theophilus, a ' crater ' in the west quadrant,
has a diameter of 64 miles, and a depth of 1,400 to
18,000 feet, perhaps the deepest of the lunar 'craters.'
In curious contrast to this is Archimedes, which,
although 50 miles in diameter, has a depth of less than
700 feet, with an interior almost quite smooth. Plato,
the conspicuous dusky spot near the northern limb,
is a walled plain about 60 miles in diameter with a
comparatively flat interior, on which, however, some
bright streaks and small * craterlets ' are visible in
powerful telescopes. Albategnius, near the centre of
the disc, is a fine walled plain over 60 miles in diameter
with a central hill and a peak on the north-eastern
border of about 15,000 feet in height. Near Archimedes

12 INTRODUCTION

are two fine ' craters ' known as Aristillus and Autolycus.
Near the western limb is a fine walled plain called
Langrenus with terraced ring of 10,000 to 15,000 feet
in height. Some distance south of this is another
fine example known as Petavius, with a wall nearly
11,000 feet high, and a central hill, so common in
these formations. Among large walled plains the
following may be mentioned : Ptolemseus, near the
centre of the disc, has a diameter of about 115 miles
with a comparatively level interior and a rampart wall
which rises in some places to a height of nearly 13,000
feet. Near the southern point of the disc is an immense
ring called Clavius, about 140 miles in diameter with
a very high wall. Close to the south-east edge of
the disc is a vast plain known as Schickard, the
diameter of which is about 130 miles. The interior
is nearly flat, and from the centre of this immense
enclosure a lunar spectator could scarcely see the
rampart wall, although rising at one point to a height
of over 10,000 feet ! Close to the eastern limb is a
very dark spot called Grimaldi, which is nearly as
large as Schickard and has occasionally been seen
with the naked eye. There are many other remarkable
ring plains on the visible lunar surface, but the above
examples may suffice for our present purpose.

4. — Valleys and Clefts or Bills. — The great Alpine
valley has been already referred to. Near the ' crater '
Rheita, in the south-west quadrant, is an immense
valley about 187 miles long and 20 miles wide. The
* Hyginus cleft ' near the centre of the disc intersects

INTRODUCTION 13

the ' crater ' of that name and runs for a distance of
about 95 miles, with a width of 1J. The Aridaeu$
cleft, which lies to the west of the preceding, is even
longer and wider. These ' clefts ' and ' rills ' form
some of the most remarkable of the lunar features,
but are sometimes so narrow as to be only visible in
large telescopes. M. Fauth has seen over 1,600.

Another interesting and mysterious feature of the
moon's surface is the system of bright streaks or rays
which diverge from several of the ' craters. 5 Of these
the most remarkable are those which radiate from
Tycho. The ' craters ' Copernicus, Kepler, and Aris-
tarchus, also form centres of rays. These bright
streaks are most conspicuous on the full moon, and
seem to pass over mountains, valleys, and ' craters '
in a way which renders a satisfactory explanation of
their nature and origin a matter of great difficulty.
Proctor was of opinion that they were formed during
the process of cooling when the lunar surface was in
a heated and plastic condition.

Near the boundary between light and darkness —
the ' terminator, 5 as it is called — there are visible in
nearly all phases of the moon bright spots within the
dark part shining like stars. These are the tops of
mountains lit up by the rays of the rising or setting
sun while the low-lying lands remain in darkness.
When fully illuminated these mountains cast shadows
which are best seen about the time of first and last
quarter.

The aspect of the heavens as viewed from the
moon will differ in many respects from that visible to
us. The stars and planets will present very similar

14 INTRODUCTION

phenomena, but owing to the absence of an atmosphere
they will shine with greater brilliancy and will be
visible in the daytime as well as the night. Mercury
especially will be much more easily seen than with us.
Stars which on earth are only visible with an opera
glass will there be distinctly seen with the naked eye,
and the Milky Way, here so dimly seen, must there
form a brilliant spectacle. But the behaviour of the
earth as seen from the moon will be wholly different
from any celestial phenomenon with which we are
familiar. It will show a disc of nearly two degrees in
diameter, or about thirteen times larger than the
moon appears to us. From any point on the visible
surface of the moon the earth will appear constantly
immovable, or nearly so, in the sky, all the stars
moving round as they appear to do on earth, but much
more slowly, the lunar day being nearly a month long.
From the centre of the visible hemisphere the earth
will appear nearly immovable in the zenith ; from
points near the edge of the disc it will appear constantly
near the horizon, and from other points it will be seen
at different altitudes varying with their distance from
the edge of the visible surface. From points on the
limb it will — owing to the variation known as libration
— be seen sometimes to sink a little below the horizon
and sometimes to rise a little above it. The earth will
show phases similar to those of the moon but in reverse
order, the earth being ' full ' at ' new moon,' and ' new '
at ' full moon. 5 Of course from the opposite side of
the moon the earth will remain permanently invisible,
in the same way that the stars near the south pole
are invisible to the inhabitants of England. Although

INTRODUCTION 15

the earth remains fixed in. the lunar sky, its rotation
on its axis, will be clearly visible, the various continents,
oceans, and islands, being seen in turn, when not
obscured by cloud, and the polar regions, of which
we know so little, might then be easily examined with
a powerful telescope. Owing to the apparent fixity
of the earth in the sky, the study of astronomy would
be, to a lunar inhabitant, beset, with many and great
difficulties. He would probably imagine that the
earth was really an immovable body in space, and the
small variations visible in its position referred to
above would only add to the mystery of celestial
motions.

The solar corona and ' prominences, 5 the zodiacal
light and Gegenschein will be clearly visible from the
moon even without the aid of a solar eclipse, and
especially just before sunrise and immediately after
sunset they will present a splendid and striking
spectacle.

In the following pages M, Fauth gives a very
interesting account of the features visible on the
moon's surface derived from observations made by
him during the last 20 years with refracting telescopes
of 6£ or 7 inches aperture. He considers the ' meteoric
theory ' of the formation of the lunar ' craters,' and
shows that a ' bombardment ' of the moon's surface
by large meteors would be quite inadequate to produce
such enormous ' ring mountains ' as some of thos$
we see on our satellite. In this conclusion I fully
concur. As M. Fauth asks, how could the earth
have escaped a similar bombardment ? He gives a
very interesting historical account of the work done

16 INTRODUCTION

in past years in the delineation of the lunar surface.
With reference to photographs he shows that, although
for the purpose of fixing the relative positions of
objects, they are more accurate than maps made from
eye observations, they are deficient in detail, and in
the sharpness of definition seen by the eye even in
moderate sized telescopes. Judging from the lunar
photographs I have seen this objection seems well
founded. Photography has certainly not been so
successful on the moon as it has been in other branches
of astronomy.

M. Fauth shows that in the large lunar ' craters '
and ring plains the proportion of depth to height of
walls is comparatively small. They are more like
shallow dishes, and contrast strongly with terrestrial
volcanoes, which are usually high cones with a com-
paratively shallow crater on the top. For this
reason he thinks it doubtful that the so-called lunar
' craters ' are really of volcanic origin. They seem
to be entirely different from the volcanoes with which
we are acquainted on the earth and may possibly
have had a different history. He calls them ' walled
plains,' and this seems a better term for the larger
objects, such as Clavius, Schickard, Grimaldi, Plato,
etc. It should be stated, however, that the late
M. Gaudibert observed some high volcanic cones on
the moon with small crater openings on the top.
One has recently been found on a photograph by
Professor W. H. Pickering about 12 miles east of Kies ;
and doubtless many selenographers will still adhere to
the volcanic theory of lunar surfacing. However this
may be, M. Fauth' s work is well worth reading by
those who take an interest in the moon.

V INTRODUCTION 17

M. Fauth favours the idea that the moon is covered
with a thick layer of ice. This hypothesis has also
been advocated by Andries and Ericson, and there
seems to be some ground for the idea, as the
temperature of the moon's surface must be very low.
M. Fauth has in preparation a large scale map of the
moon which will show an enormous amount of detail,
and will certainly, I think, be more reliable than any
photograph hitherto taken. From this elaborate work,
any suspected changes in lunar topography in future
years may be either verified or disproved.

J. ELLARD GORE

PREFACE

The science of the moon cannot yet be said to
have been elaborated in proportion to our material.
Though the works issued in the last two decades have
not been few in number, and, even taking full account
of the marvellous results obtained by the application
of telescopic photography, far from slight in quality,
still, the peculiar conditions under which the structure
of ' Selenography ' is slowly rising have not facilitated
publication. In Germany the only works recently
issued are my 'Atlas,' with the textual explanation
(1895), and the first volume of Krieger's 'Atlas,' (1898).

My maps were meant in the first place to show how
to complete the study of the moon's topography, and
they give a much more extensive and accurate picture
than the existing maps. Krieger went on to explore
a large number of craters and rills by means of
excellent enlargements of photographs, and by making
models of them. He has died since, and I have
myself pressed on with the topography of the moon on
a large scale. With the use of good instruments
(objectives by Dr. Pauly, of Jena), under good con-
ditions (my observatory has an altitude of 450 feet),
I have penetrated into the features of the moon's face
to an extent that no other eye has yet done, and that
has surpassed all my own expectations. I owe a great
deal to the liberality of the Zeiss Institute, which lent

20 PREFACE

me the use of a good modern objective of 7 inches
aperture from 1896 to 1903, at the request of Dr. Pauly.
To this fine instrument I owe the discovery of thousands
of small objects, an invaluable exercise in minute
vision, and a very useful experience in appreciating
lunar forms. My own objective has an aperture of
only 6 \ inches. I have, after 17 years' use, grown to
love it, as one does love such instruments, for the
endless intellectual enjoyment it has afforded me and
the work it has done for Science ; yet I have regretted
that I was unable at times to apply a more powerful
instrument. Not that I desired to posess one of our
giant telescopes ! I have often felt that I could work
with more success than the observers at larger instru-
ments. But, as I have got to the limit of my faculties,
and my apparatus can hardly show me anything new
in the regions I have studied, it might be possible for
me, under better conditions, to determine certain
points of great interest in the development of selenology
and of cosmology generally. That would only
indirectly be a personal merit, since I have an eye
that is remarkably adapted in structure for such
research, and has improved more and more with
use in the power of perceiving tiny features. Hence,
I should hope, with a large instrument, to make maps
(on the scale of our large general maps) of certain
localities on the moon which it is most important to
explore both for the sake of lunar science and of
science generally.

The present work is issued in response to an
invitation to tell the story of the development of lunar
science. Only those who know well the limitations of

PREFACE 21

this subject will venture to look beyond the sparse
material of the present into the future, and back into
a past on which careful study can throw much light.
There are plenty of historical bye-ways even in our
limited field. They can be followed in any technical
work on the moon, and they afford a good deal of
historical material, as well as an interesting glance at
the modest workshops, and still more modest inventory,
of early explorers. But we do not find a critical
appreciation of the material already acquired, a study
of lunar problems based on personal vision and sup-
ported by long years of experience.

Probably there never were so many hypotheses
floated in regard to the riddles of the moon as in the
last few years ; but they have not advanced our
knowledge, because, though theoretical students were
plentiful enough, the practical observer was not. It
is quite certain that a man who is not familiar with
the actual moon, and only interprets photographs,
knows as little about it as one who would try to learn
the taste of fruit from a picture. The greatest German
selenologist, J. Schmidt, has expressed himself on this
point in words that should be taken to heart. It is
equally clear that the time has gone by when a man
could pass as a specialist on the ground of literary
work alone. The work to be done to-day is practical :
to throw light on what has been acquired and show
how the field must be worked with new success.

I trust the attentive reader who is making his way
through a material that is unfamiliar to him will
realise, from the pictures and maps of the work, how
much ground must be covered before one can appreciate

22 PREFACE

certain lunar forms, and what an enormous amount
of detail-work we have succeeded in doing. I go more
fully elsewhere — especially in the astronomical journals
— into particular problems, and trust that, with text
and pictures, I can give even the uninitiated a clear
idea of what are called the ' changes ' on our neighbour
planet. In the special maps which have been prepared
from my own photographs (though, unfortunately,
reduced to a very small scale), one can pretty well
see the limits of my means of research. Further, I
give an account of the most recent work in the science
and a glance at the questions that press for solution
in the future, in order that we may understand the
matter that forms the outer shell of our satellite.
Unfortunately, the twentieth century has not yet
constructed the new map of the moon which I projected
six years before it commenced. May it be included
amongst the achievements of the future ! The chief
aim of my little work is to prepare the way for it, and
point out the direction of research.

PH. FAUTH

THE MOON 27

Fig. 2. — Photograph of the full moon for comparison.

been humorously, and not ineptly made. All these
things are only indications of the habit of reading
some expression or other into the unknown.

But an explanation of the moon that went beyond
all these imaginative conceptions, a physical explana-
tion, was attempted by the ancient Greeks (Clearchos ?),
when they conceived the moon to be, possibly, a
concave mirror reflecting the image of our earth. The
idea came from Persia. Anaxagoras regarded the
moon as a sort of earth with hills and valleys, and
was banished on account of the independence of his
speculations. Plutarch very accurately compares the
shadow of the high lunar mountains, as it is seen with
the naked eye in the irregularity of the light-line or
terminator, at the first quarter, with the shadow of
Mount Athos, which sometimes reached as far as the
island of Lemnos. Thus from the constancy of the
design and its finer features it was possible to form
a substantially correct idea of the nature of our
companion's surface and a fair appreciation of lunar

v% jfi v»2i

^bKvvXI

It '

■ffvHR

L^i

AT' E&Cfl

EyS

an ^ "*' n

Fig. 3. — The Apennines and the walled plain of Archimedes,
(from A. Mang and Ph. Fauth's Quadrantenfevnrohr, <kc.)

THE MOON 29

forms, so that people began to speak of a round body
with mountain-like processes on its surface. But
neither the Greeks nor the Oriental races made any
further progress, and the Romans failed to do anything
in the matter.

The next step came with the invention of that
wonderful instrument for bringing distant objects
nearer to us, the telescope (1608)*. We can easily
believe that, after the first gratification of curiosity
on indifferent objects, the moon would be one of the
earliest things in the heavens to attract the attention
of the lucky inventor. But it took the great mind of
Galilei to give meaning and name to the new spectacle.
That he left only an imperfect sketch of the new
world is due to the fact that the whole field of celestial
observation was opened to him at one stroke ; he was
too overwhelmed with new discoveries to go thoroughly
into any single one. The improvement of the telescope
by Kepler confirmed Galilei's ' round mountains ' on
the moon, and Kepler expressed his astonishment at
their number and structure. The burgomaster of
Danzig, Hevelius, left behind him a series of drawings
of the moon's phases, which he had obtained with a
telescope magnifying forty times ; we have also views
of the full moon from him (1645), and one from Fontana
(1630). We know also of a large general map by
Langrenus (1645), and one by Grimaldi (1665), which
was published by Ricciolif. But the imperfect instru-
ments only gave very poor enlarged pictures of the
moon, and at that time it was usual to compare our

* On October 2nd, 1608, Jan Lapprey (Hans Lippersheim or Lipperseim)
attempted to secure a {Mitent from the States General of the Netherlands.
On October 17th, Jacob Metius made another attempt ; and in 1609 Galilei
heard of the invention, and succeeded in making one. He was the first to shew
how to prepare telescopes, and use them for astronomical purposes.

t Fon tana's map may be seen in Flammarion's La Planete Mars (p. 10),
and in W. Meyer's Dan Weltgebaude (p. 94). Hevel's map also is given in the
latter work (p. 95). Langrenus's map is reproduced in del et Terre (vol. xxiv).

30 THE MOON

satellite to over-ripe cheese or pumice-stone. Further
progress depended on the improvement of the telescope.
The next step in this was the making of lenses of
enormous focal length, which gave clearer images with
less colour at the edges of bright objects. We can realise
the action of these contrivances by using a spectacle
glass (costing a few pence) with a four yards focus.
A flat lens of that kind will give a focal image of the
moon more than an inch large.

With instruments of this kind, Robert Hooke and
Dom. Cassini did their work, the latter publishing in
1680 a map of the moon about twenty inches in
diameter. His contemporary, Isaac Newton, sought
to do away with the inconvenience of the long tube
by using concave mirrors for producing the image, and
the metallic mirrors that were made in increasing
quantities towards the end of the 18th century did
such good work that the lens was almost forgotten.
Further advance in the manufacture of glass objectives
was needed, and this was sketched by the mathema-
tician, Euler, in 1747, in the sense that the colour-edge
of the lens-images was to be got rid of in some way.
In point of fact, the optician Dollond was the first
to produce an ' achromatic ' telescope by the com-
bination of two lenses, in 1758, though as the result
depends on the testing of many different combinations,
these ' achromatic ' instruments were far from perfect.
Still they were successful rivals of Herschel's numerous
' reflectors,' which were very good of their kind. In
England the heavier reflectors were generally used,
but in Germany the smaller and more convenient
Dollond-achromatics were more accepted.

What Herschel did with his mirrors for stellar
astronomy in England, was done for the science of the
moon by Schroeter in Germany He made a number
of J interesting observations ; and, if his skill as a
draughtsman had been at all equal to his power of

THE MOON 31

observation, his pictures would still be valuable. But
he was so far led astray by his possession of powerful
optical apparatus as to go beyond the problems of
his time, and occupy himself with ' changes ' in the,
as yet, unworked field, instead of laying the foundations
of a sound science of the moon according to the power
of his telescope. The distinguished astronomer, T. Mayer
of Gottingen, who made careful measurement of the
moon's surface and drew an eight-inch map of
the moon, published a work (1775), that remained the
sole accurate map until 1824. Schroeter's partial
pictures could not be combined into a general map,
because he had pursued a misleading purpose. More-
over, the means at hand were not very liberally used
in the exploration of the moon. Apart from the
comprehensive genius of Herschel — and even he only
did so intermittently — no one used the best instruments
of the day on the moon. There were greater problems
to be attacked in the fixed stars, and hardly a single
professional astronomer concerned himself with our
nearest neighbour.

Once more progress depended on an improvement
of the instruments. Fraunhofer's theoretic insight
into the conditions of the making of achromatic lenses
and his success in making glass combined in the nine-
teenth century to produce instruments far beyond
Dollond's. On the 18th of December, 1817, glass was
melted to make an ' achromatic objective ' of unheard
of dimensions — 10 inches diameter and 14 feet focal
length — and the telescope, afterwards installed at
Dorpat, then at the beginning of its work, was regarded
in England as something fabulous. Even when
gigantic refractors of 13 — 20 inches aperture followed
— to-day they exceed 40 inches — the poor moon was
still neglected, and remained the field of wealthy
amateurs. At Dresden, the geometrician, Lohrmann,
worked so zealously in private at the task, that he

32 THE MOON

formed a large map of the moon, based on his own
measurements and drawings, and published it in four
sections, with text, in 1824. In 1857 Beer andMadler
published an equally large map and a complete
' selenography,' most of the work being based on
Madler's private study in his friend Beer's modest
observatory at Berlin. After these we find a number
of people, such as Kinau, who, partly for their own
pleasure, and partly for the advance of science, investi-
gated the moon with the aid of the incomparable
telescopes of Fraunhofer and his successors. The
distinction between professional and amateur astro-
nomers became greater during the course of the
n'neteenth century. The work of observing, drawing,
and describing was left to the latter, and hence the
physical features of the planets generally, especially
of our moon, were generally taken up by industrious
and able amateurs.

In the second half of the nineteenth century it
was suddenly discovered that there was a new and
far-reaching interest in our neglected satellite. A
young enthusiast mounting his poor telescope on a
lamp-post to get a glimpse of the wonders of the
moon, was so profoundly impressed, that he con-
tinued throughout life to gather material. He
became a ' selenographer,' went far beyond Lohrmann
and Madler, and about the close of his life (1878)
published, at the public expense, a map, twice the
diameter, four times the surface, and seven times as
rich in detail, as Madler's ' Mappa Selenographica ' ;
though the plan of this gigantic map was very different
in his mind from what he actually achieved, and the
life of one man was too short for the work of mapping
out the moon on the scale that the optic appliances
of his time permitted.

Thus appeared the finest piece, as yet, of lunar
research, the ' Map of the Mountains of the Moon,'

THE MOON 33

by Julius F. J. Schmidt, but new circumstances arose
that demanded a fresh attempt. The work to be done
is not merely to ascertain the features that certain
agencies have induced in the face of our satellite. It
is equally necessary to have an elaboration and control
of the material by many co-operating students. A
very welcome advance in optics has provided the best
instruments at a moderate price, and the spread of
scientific education in the last few decades has stimu*
lated interest in the observation and reproduction of
the cosmic bodies. In addition, a series of observers of
great merit have, by their example and teaching,
created a school of good amateur astronomers, and
the multiplication of scientific periodicals has contri-
buted by announcing the latest news from the heavens,
fostering investigation, and allowing even the amateur
to have his say. The science of the moon became once
more the province of amateurs with the work of
Schmidt, and that is a circumstance of great influence
on the attainments that we have made. At this stage
of peaceful development and interpretation we find
accomplishments that have greatly extended our
knowledge. In California a great 36-inch refractor
has been established by a private donor, Mr. Lick,
and used in photographing the heavenly bodies,
especially the moon*. A still larger (40-inch) refractor
has since been set up at Yerkes Observatory, Chicago,
through the munificence of another private donor. An
immense number of negatives of all its phases have
been taken and published, and we have every hope
now that the riddle of the moon's sphinx-like face will
soon be solved, t

* (See * Brief account of the Lick Observatory,' by E. S. Holden).

t See the Photographic Atlas of the Moon from the Lick Observatory, with
19 plates on the scale of Madler's map. The figures vary considerably in
fineness, but have a remarkably good tone.

34 THE MOON

With our more accurate knowledge of the topo-
graphy of our satellite there has been no lack of attempts
tp Interpret its peculiar condition. The resemblance
of lunar structures to the craters of volcanoes, like
those on our planet, was too great to resist the temp-
tation of giving that name to them and endeavour
to explain them as such ; in fact the almost circular
shape of all of them seemed to demand some such
explanation. Hooke long ago experimented with
molten alabaster with the object of proving that the
round mountains of the moon might have been formed
by heated vapours issuing from its glowing interior,
perforating it, and throwing up walls. We know now,
however, that the cohesion - of matter is not great
enough to permit the formation and distension of
bubbles .of 60 miles and more in diameter. The
volcanic theory of the formation of the lunar type of
mountain was afterwards attacked by Kant. He
would not hear of ' craters,' but believed that certain
terrestrial districts, such as Bohemia, threw some light
on the structure of the lunar rings. Kant, however,
overlooked the fact that only a few terrestrial structures
can be compared with the tens of thousands of ringed
walls, and so the moon remains a different and very
distinctive world.

Schroeter returned entirely to the volcanic theory
in his search for ' changes,' which he believed he
discovered on a gigantic scale. Herschel speaks of a
fiery eruption on the dark side of the moon, which he
followed with his own eyes ; no doubt the use of his
great reflecting telescope, with slight magnification,
might very well give the dull glow of a highly reflective
spot the sparkling appearance of a star. Other
extraordinary features have been attributed to the
moon since Herschel and Schroeter, because it was
not sufficiently known at the time how to distinguish
recurrent monthly phenomena from accidental and

THE MOON 35

momentary ones. Beer and Madler, two industrious
collectors of facts, went deeper into the knowledge of
its features, in spite of their small instruments*, than
their predecessors ; and they knew nothing of
4 changes.' Indeed, in view of the immature condition
of * selenography ' they do not attempt to set up a
4 selenology,' as they would have had a right to do.
Humboldt also recognised that the volcanic theory
does not apply to certain localities.

The sphinx-like face of the moon, its surface
covered with hieroglyphics, remained unexplained for
many decades. Then the cooler attitude of th^
founders of modern selenography was assailed by a-
new volcanic theory, worked out with great energy^
and conviction. Two English scientists, Nasmyth and.
Carpentert, had gone deeply into the features of our
moon with their large reflecting telescopes. They*
made some ingenious models, and at length reproduced
the finest details of lunar relief in a preparation of
plaster of Paris. When a vivid light was thrown on
this model, it had a most deceptive resemblance to the
lunar landscapes, as they are seen in the telescope.
But the resemblance could only deceive the inexpert.
The otherwise conscientious observers were not able to
refrain from introducing their favourite theory of lunar
volcanic energy into their model-relief . Thus we find
them, in the second half of the nineteenth century,
with a good deal of sagacity and technical and empirical
knowledge, attempting to prove what they would like
to see proved, yet completely f ailing in the end. Their

* Madler's Fraunhofer of 4 in. aperture and powers of 140 and 300 was a
fine instrument ; but we now use lower powers, and get clearer and better
views. Madler generally used a power of 300 with an objective of 4 in. aperture,
but the present writer has worked for years with powers of 160, 176, and 210,
with objectives of 6£ and 7 inches. Many of the peculiarities of the earlier
science are due solely to excessive magnification. Lohrmann's telescope was
larger, but perhaps not so good.

T ' The Moon, as Planet, World; and Satellite,' 1884.

THE MOON

scientific conscientiousness compels them to admit
that their knowledge is imperfect here and there.
They feel themselves that precisely those objects that
-are most distinctive and most in need of explanation
«do not find a place within the frame of their theory
of the origin of lunar mountains, and that the largest
^nd the smallest of the typical circular structures are
not susceptible of explanation by it.

Yet all the contemporary and later * selenologists'
Btart from the same point of view. The less they know
of practical observation of the moon in detail, the more
they seem prepared to solve its riddle. Amongst a

Fig. 4

Fig 5

Fig. 6

Imitation of lunar craters in ground felspar by Meydenbauer. Fig. 4 :
flat twin-crater. Fig. 5 : strongly developed wall with secondary inner crater
Fig. 6 : locality rich in craters.

large number of attempts in this direction we may
select three for notice. Meydenbauer (Figs. 4, 5, 6)
began with the intention of explaining the origin of
walled depressions by the fall of meteoric bodies, and
really produced structures resembling those in the moon
by letting small quantities of dust fall on a layer of
dust. W. and A. Thiersch developed this aggregation
theory in a special work ; and there seemed the more
reason to oppose it to the volcanic theory as we were
learning more and more every, day about the presence

THE MOON 37

of countless meteoric bodies in space, and the extension
of the theory of cosmic swarms of meteors to another
province — the meteoric nature of Saturn's rings had
been affirmed and proved — was supported by the
leading authorities. Hence it seemed as if meteoric
masses falling on the moon had led to a reaction of its
crust — the formation of ring-mountains and the out-
pouring of the molten interior.

As if the volcanic basis of this view were not pre-
carious enough, the theory of aggregation brought fresh
difficulties. The chief objection to these speculations
is that the tens of thousands of lunar structures demand
that these meteoric impacts should be vertical, or in the
direction of the moon's radius ; and we can demon-
strate on mathematical grounds that a vertical impact
is almost impossible in the case of a body that is without
a buffer in the shape of atmosphere. It is therefore
quite certain that these impacts did not occur in tens of
thousands. It is much easier to speak of a bombard-
ment of the moon's crust by meteoric projectiles than
to prove it ; and it has certainly been forgotten that
the sudden arrest of a cosmic movement at the rate of
ten or twenty miles a second would cause an enormous
generation of heat, so that a meteor would neither
dig up the material of the moon, nor deposit its own
material in a circular mound.. The visible product of
any such meteoric impact would rather be a spot molten
with the heat and traces of the explosive expansion of
the vapourised mass of the meteor — an indication of an
explosion, but not a circular mountain. There is no
reason whatever to suppose that larger and more nu-
merous bodies dashed on the moon in former ages than
in ours ; nor is it explained why the moon alone is so
pock-marked, while the earth, which is far more active
in attracting foreign bodies shows no trace of impacts.

No more substantial ground can be found for the
views of geologists like Professor Suess or Toula.

38 THE MOON

Whether it was volcanoes alone that formed the moon's
surface, or whether meteoric impacts were needed to
relieve existing Strains, or whether the ageing moon pro-
duced the mountains by the wrinkling and breaking of
its crust, so as to release the molten matter within,
which would remain visible in the round hills — in all
these speculations there is at the bottom a disputable
hypothesis, the Laplacean theory of the formation of
the solar system. This theory has lost much of its
prestige of late and we often find its untenability and the
scantiness of its support in recent research openly ad-
mitted even in professional circles.* Loewy and
Puiseux, it may be said, take their stand on the old
ground in their explanation of the maps in their Paris-
ian ' Atlas of the Moon.'

If we glance back at our historical survey, we find
that there were two circumstances that hypnotised the
founders of selenologies — of whom Nasmyth and Car-
penter were the only ones with a real knowledge of the
moon — so that they were incapable of paying attention
to its real features. The first of these was the circular
form of the so-called craters ; though on closer exam-
ination, and on the confession of the theorists themselves,
they are found to have a somewhat different com-
plexion. The volcanoes of the moon are hollowed out
like saucers, while those of the earth rise up like moun-
tain cones : the former are of gigantic dimensions, the
latter would be barely perceptible if they were removed
to the moon : the former consist only of a circular
mound, the latter almost always form a cone. The
other circumstance was the general acceptance of the
Laplacean hypothesis of the origin of the sun and planets.
In the days of its founder this system was probable
enough ; now that our knowledge has so much in-
creased, it not only fails in its older form to harmonise

* See Riem's article ' Die mcdenien Weltbildungslehren ' in the July
number of Gluuben and Wiwtn, 1905.

THE MOON 39

with astronomical truths, but it offends against fund-
amental laws such as the persistence of force and can
render little help to cognate sciences; such as geology,
meteorology, and palaeontology. We are, therefore, in a
stage of transition to-day — not alone in regard to lunar
science — which must end in a rejection of Laplace's
theory in its first form. Only when we have rejected
untenable foundations will it be possible to pursue our
task with any profit and read the language of the
moon's surface.

The direct inspection of the moon with a telescope
and the drawing of small parts on a large scale were
not likely to lead to an abandonment of the old views.
More confidence was felt in the impartial results of
photography, in view of its fidelity and its effectiveness
in two directions. In the first place the telescope only
shows a small part of the disk at a time, and the varying
illumination and the almost constant agitation of the air
only allow us to examine particular spots. Once the
opportunity is past it will be many months before the
spot is illuminated in much the same way, and then
clouds or other impediments may prevent us frorti
examining it. Photography, on the other hand,
would enable us to attain results in a short time that
would have taken years at the telescope. Further, it
is no longer the province of the astronomer alone, or
even the amateur, to work up lunar experiences into
a large scheme of another world. A whole crowd of
specialists in different branches of science get pretty
much the same view of the external features on which
the theory and analogy are to be based. This had never
been the case before, and so much was expected from
the judgment of geographers and geologists.

The ' daguerrotype ' had hardly been invented
when an enterprising American, Dr. John W. Drayer,
of New York, began a series of pictures of the moon
on silver plates (1840). Ten years afterwards, the

THE MOON

photographer Whipple, began, at the invitation of
William C. Bond, director of the Harvard Observatory,
to work with the Merz refractor of 15 inches aperture,
and produced images more than two inches in diameter.
Another American, Humphrey, obtained even better
pictures of the moon with a two seconds' exposure,
showing a good deal of detail ; and at Konigsberg, in
Germany, Barkowki secured negatives that would bear
enlargement up to two inches. But a great advance
was made by Warren de la Rue, at London, who began
his work in 1852, especially when, in 1857, he caused
his telescope to follow the movement of the moon by
clockwork. His pictures were good and numerous, so
that he could make a selection of them, and arrange
them in pairs to produce stereoscopic effects and
represent the moon as a globe. Dr. Henry Draper,

Fig. 7 Fig. 8

Two photographs of the full moon for the stereoscope.

of Hastings (on the Hudson), who united in himself
the attainments of the chemist, physiologist, photo-
grapher, optician, and constructor, made a metallic
concave mirror in 1860, and one -of silvered glass in

THE MOON 41

1861, each 16 inches in diameter, and worked with
unprecedented success. One of his photographs of the
moon, an inch in diameter, taken in 1863, was enlarged
to the size of Madler's 3 foot map, and was still de-
cipherable. In 1870, the indefatigable worker made a
speculum twenty inches in width, but after 1880 he
used — with more advantage — a refractor made especi-
ally for photographic purposes, with a 12 inch objective.
Rutherfurd, of Cambridge (U.S.), had observed in 1857,
that there was a difference of f of an inch between the
distance of the image for the eye and for the sensitive
plate in his telescope.* Once this was taken into
account pictures of the moon were secured that
could be enlarged to five inches. He also constructed
his first stereogram, independently of de la Rue.
He further tried to increase the sharpness of the
image by separating the lenses of his four-inch objective
about ^ths of an inch. A large objective (11 inches in
diameter and of 14 feet focal length) gave in 1864 a pic-
ture of the full moon which showed details very sharply
even when enlarged to seven inches. Another objec-
tive, specially corrected for chemical rays, gave him in
1865 a focal image of fths of an inch, which could be
enlarged with success to 21 inches ; and after 1871 he
used a 13 inch refractor. Beside these successes we need
pay little attention to the work of Wolf and Rayet
with a seven inch reflector or even of Ellery. (of
Melbourne) with a 4 foot reflector, which gave direct
images of three inches diameter. But the Argentine
astronomer, Gould, succeded at Cordova in 1875, with

* Spitaler says that the lenses of a large refractor show a focal difference
of about one inch between the optical and the chemical rays. ' The sensitive
plate could be pushed |th of an inch to either side in the chemical focus
without making any perceptible change in the quality of the photograph.'
Even in six-inch telescopes the difference between the two foci may amount to
more than $ths of an inch, so that for photographic purposes it is necessary to
achromatise for the chemical rays or to use reflecting telescopes, which give
colourless images.

42 THE MOON

the help of a pupil of Rutherfurd's, in producing orig-
inal pictures of an inch and a half, which were enlarged
to nineteen inches.

The year 1888 saw the beginning of the work of
the great Californian telescope. For photographic
purposes the great 36 inch lens is converted into an
enormous camera of 33 inches aperture and 50 feet
focal length. This gives a focal image of the moon's
disk 5 inches wide. Unfortunately, the best results
are not obtained with the full aperture, but with one
shortened to 8 inches. Burnham, Schaberle, and
Campbell, in particular have secured a large number of
plates of all parts of the moon with this instrument.
In the meantime, the brothers Paul and Prosper Henry
had done good work at Paris with a 13-inch objective
of their own make. They began to photograph the
moon before the erection of the Lick telescope, pro-
ducing a large original image by means of intermediate
lenses. Other experiments were made by Prinz at
Brussels, Pickering at Cambridge (U.S.), Spitaler at
Vienna, and Wolf at Heidelberg*. But from 1890
onwards, the Henry's secured pictures that astonished
all students. Still it was some time before the method
of direct magnification of the image was generally
preferred to focal photographs. The dry plates contain
fine grains of silver precipitate in the film. Details
finer than these cannot be shown, and when a negative
is enlarged we see the crudities that result from this
granular nature of the film. This defect marred the
otherwise remarkably good Lick photographs. When
Prof. Weinek put them under the microscope he could
discover nothing more than was visible on a careful

♦For Pickering's work see 'Annals of the Astronomical Observatory of
Harvard College,' vol. xxxii, part 1. Prinz used an aperture of 9 inches, and
had an image of 4-13 inches : Pickering used a 33-inch aperture, and enlarged
the full moon to 28-70 inches : Spitaler used the 27-inch Vienna refractor,
Wolf his own 6- inch refractor.

THE MOON 43

mechanical enlargement of the plates. When he did
fancy he had discovered further and finer details, it
turned out to be an illusion, as it had been pronounced
from the first by those who were well acquainted with
the moon*.

Thus, for instance, the magnification of the round
mountain Capella, and the small parasitic crater
Taruntius C, shows a number of fine lines, which no
expert now regards as ' rills.' We also see a large
number of craters and fine bubbles which are in marked
contrast, on account of their sharp definition, to the
remarkable vagueness of all the large details that we
know. It is a difficult task to interpret these details ;
and it is equally vain to attempt to-day to determine
the causes that have been at work in the glass of the
positive, the sensitive film, or the taking of the negative,
to produce these apparently well-defined craters under
the microscope. We have learned from Prof. Prinz's
measurements that even objects twice or many times
the size of those supposed to be found in the photograph
under the microscope are altogether vague and in-
definable on the same plates.

Meantime the Lick plates were enlarged very
considerably, and an atlas of 19 plates was published,
on the scale of Madler's map, but the details are largely
spoiled owing to a defect in the method of taking the
originals. Then Prof. Weinek began his magnifications,
and published an atlas of 200 wonderfully beautiful
plates of the moon, which were evidently made with
the utmost care from the Lick photographs. About
the same time Loewy and Puiseux began to work at
Paris with a particularly suitable instrument with a
24-inch objective and 60 feet focal length. They took
focal negatives, which hardly needed one second
exposure, and measured up to seven inches in diameter.

♦See 'Publications of the Lick Observatory,' vol III, 1894 : with 16
plates, including 11 heliogravures.

34 THE MOON

With our more accurate knowledge of the topo-
graphy of our satellite there has been no lack of attempts
tp Interpret its peculiar condition. The resemblance
of lunar structures to the craters of volcanoes, like
those on our planet, was too great to resist the temp-
tation of giving that name to them and endeavour
to explain them as such ; in fact the almost circular
shape of all of them seemed to demand some such
explanation. Hooke long ago experimented with
molten alabaster with the object of proving that the
round mountains of the. moon might have been formed
by heated vapours issuing from its glowing interior,
perforating it, and throwing up walls. We know now,
however, that the cohesion . of matter is not great
enough to permit the formation and distension of
bubbles .of 60 miles and more in diameter. The
volcanic theory of the formation of the lunar type of
mountain was afterwards attacked by Kant. He
would not hear of * craters,' but believed that certain
terrestrial districts, such as Bohemia, threw some light
on the structure of the lunar rings. Kant, however,
overlooked the fact that only a few terrestrial structures
can be compared with the tens of thousands of ringed
walls, and so the moon remains a different and very
distinctive world.

THE MOON 35

momentary ones. Beer and Madler, two industrious
collectors of facts, went deeper into the knowledge of
its features, in spite of their small instruments*, than
their predecessors ; and they knew nothing of
6 changes.' Indeed, in view of the immature condition
of * selenography ' they do not attempt to set up a
' selenology,' as they would have had a right to do.
Humboldt also recognised that the volcanic theory
does not apply to certain localities.

t ' The Moon, as Planet, World; and Satellite,' 1884.

Fig. 10
The round mountains, Janssen and Fabricius (1 mm. = 1800 m.)

THE MOON 47

over the moon, unless it is examined at full. It need
not be said that the finest pictures can only give a
clear reproduction of the middle tones. What the eye
takes in at a glance can only be gradually reached by
the photograph. For every photograph that turns out
' good ' with one second exposure there are two others,
one of which perhaps needs a tenth of a second, and
the other five or more seconds exposure. If the bright
spots must not be over-exposed and the dull under-
exposed ; if they are not to be sacrificed to the spots
of medium intensity, we should need three different
and wholly impracticable photographs. Yet the human
eye takes them all in at once, without any gradual
adjustment.

Thus, selenologies that are based on photographs
are open to question. If it is ever necessary to go. into
detail, this is certainly the case as regards the moon.
Its riddles only begin to dawn on us when we turn
from the broad features and general configuration to
study the specific lunar peculiarities of the small
structures and parts of the whole. We have realised ^
that the circular shape and the walls cannot give us
any satisfactory information of themselves, and we.
have seen that there are a dozen or more hypotheses
framed on these purely external features, because a
great number of different agencies might have produced
them. The salient feature is not the ' crater,' but a
different thing altogether, that can only be explained
by a close scrutiny of the floor of the moon. Yet
scarcely one eye in a hundred is directed to the empirical
study of it*.

* See, for instance, the work of expert lunar observers who have attained
only moderate results with very large objectives I need only refer to Neison's,
Pratt's, and Klein's pictures of the Hyginus district : Neison's four pictures
in Meyer's Weltgebdude : Smyth's picture of Copernicus : Nasmyth's Tycho
region (in which it is impossible to identify the score of large craters, or even
Tycho itself) : Secchi's Copernicus (' The Sun ')- : Neison's Godin-Agrippa
landscapes, Copernicus, and two pictures of Plato : Trouvelot's landscape's of

48 THE MOON

Although photography has eclipsed the army of
once active ocular observers, who think they have been
superseded, there have been efforts made in the last
two decades that seem to show that it is possible to
do more than photography can do. With all our
precautions we have not yet succeeded in taking
plastic objects of about a mile in extent in photographs
in a properly recognisable formf. It is not enough
that we can just point out the features ; in 99 cases
out of a hundred we shall be wrong or uncertain. But
the eye can, under moderately good conditions, perceive
things and judge their size, posture and shape, when the
photographs will give. nothing but a hazy spot. In
other words, ocular vision is clearer, truer, and finer,
and is able to penetrate precisely into those regions
which it is indispensable to explore if we are to have
a sound theory of the moon.

Since Schmidt's large map was made (1878),
Klein (of Cologne) has attained some moderate results
in certain lunar districts with a 6 inch telescope,
Gaudibert (of Vaison) was equally limited in his results
with 8-10 inch silver reflectors, Elger (England) did
some work in the same direction. All these efforts

Parry, Arzachel, Gassendi, Eratosthenes, and Caesar: Trouvelot's.Linne, and
Herodotus : Nasmyth's Gassendi (in * The Moon ') : Stuy vaert's 50 lunar
landscapes : Prof. Weinek's artistic pictures, &c. I say nothing of pictures
of this kind in the Bulletin de la Soc. Astr. de France, and the Memoirs of the
British Astr. Ass. In all these pictures, though they have appeared since the

freat ' Map of the moon ' was published, you will look in vain for details that
ad already been charted, to say nothing of others. On the other hand our
special maps give fresh material every time, even in reduced forms.

t See articles in del et Terre, 1889, December, 1890, and January, 1891
Prof. Weinek himself writes in it as follows (February, 1891) : * Every competent
student knows that the image seen in the lens is still more definite than that
on the best photographic plates . . . The practised eye of the observer will
always retain its rights ; the two methods, optic and photographic, will not
exclude, but complete, each other . . . Still, they [the negatives] have clearly
proved to me that we must be very careful in discussing the smaller photo-
graphic details, and that it should only be attempted when we have two plates
taken in the same night.' Other articles in del et Terre are of November, 1892,
and 1896 : and the Bulletin de VAcad. Roy. de Bruxelles t 1892 and 1895. See
also Prinz's De Vemjploi des photographies stereoscopiques en sde'nologie.

THE MOON 49

have ceased with the recent advance in photography.
It was left to amateurs to take up the moon as a
welcome field when the plan of a fresh exploration, with
the view of forming a new map, was formulated by
the present writer.

Brenner (of Lussinpiccolo), using his 7-inch
refractor in the unique climate of the Adriatic, dis-
covered a number of very fine lunar features. Krieger
set up an observatory at Trieste with the object of
making a statistic collection of small details from
copies of lunar photographs (the Trieste Atlas of the
Moon). Others, such as D. Nielsen, of Copenhagen,
and J. Meller, of Osterath, published drawings in colour
or tone, with shadows of lunar landscapes. Then the
observatory established on the hills, near Landstuhl,
by the author, began the preparatory work for the
projected new map of the moon. Maps were made
on a scale of 10J-57 feet for the moon's diameter.
They contain an amount of detail beyond any yet
published, of which the photographs give no trace.
We have lately heard from the astronomers of the
Harvard, Lick, and Yerkes observatories of new
observations*. It seems that they are now using
their large visual instruments in the long-neglected
systematic study of the moon, and are discovering
details that had not hitherto been seen. That is very
natural in view of the hundreds of thousands of details
that are accessible to-day, and certainly a large
telescope should show more than a smaller one ; yet
the transatlantic astronomers are hardly in advance
of those of central Europe, as they seem to be un- tV
acquainted with what has been done over here for a
long time.

* Prof. Pickering ' Annals, &c, of Harvard College,' vol. xxxii. Also
articles in Sirius, 1901, viii andix ; 1902, x ; 1904, vand xii ; and 1905, iandii."
E. E. Barnard writes in the Astronomische Nachrichten (nr. 4075, February,
1906), on ' Periodical changes in the size of the glow surrounding the lunar
crater Linne.'

THE MOON

This is clearty seen from Professor Hclden's
application of the 36-inch Lick refractor to the regions
of the Hyginus and Ariadaeus rills. The eight pictures
obtained in November, 1889, are very faulty and poor
in detail (as also are the enlargements from 270 to 600)
in comparison with the large aperture and light-power
of the telescope. In the last few years, Professor W.
Pickering has explored the region of Messier with his
powerful instrument, but, in the opinion of German
selenographers, with just as little success. At all
events his picture of the two craters is not of a nature
to justify even the slenderest anticipations from such
work. He had in the spring of 1893 examined the
variations of dark spots at various points on the moon,
using a magnification of 345 to 714 with the 13-inch
Boyden telescope. The reader will see from the
comparison of the Alphonsus spots, which we give
later, how much he discovered, and how much the
present writer had done with an instrument only half
as large and a magnification of 160 to 210. It will
give a good idea of the controversy about these spots.

/• bkm

» to it

M \.V' : ' ; " ! m w*

'xm, Y~*- ''*'-•'-•

Fig. 1 1
Fig. 11.— Pickering's plan.

Fig. 12
Fig. 12 -Fauth's map.

A little earlier Professor Pickering made a detailed
study of the little craters in the depths of the circular
plain Plato, which we reproduce here, indicating the

THE MOON 51

wholly or partially certain, and the altogether uncertain
positions, together with our own map of the interior
of Plato. Most of the positions are illusory and do
not correspond to real objects, for Pickering con-
scientiously used the results of even the most superficial
of previous observers, such as Neison, Elger, Pratt, etc.
It would have been wiser to separate the chaff from
the wheat. "n

To sum up, we have some works of great value,
especially three orginal maps of the moon (Madler's,
Lohrmann's, and Schmidt's), which reflect great credit
on the conscientiousness and self-sacrifice of their
authors, and three photographic atlases of the moon
(Lick, Prague, and Paris), besides the Harvard atlas
of lunar phases*. But the ultimate aim of all these
efforts, the explanation of the processes that have left
these traces on the surface of our satellite, has not yet
been attained, chiefly because students have not yet
succeeded in emancipating themselves from the deep-
rooted but more and more untenable idea that the
matter of our solar system is still in its youth. In
this we sufficiently indicate the path and the duty of
all future study.

If we wish to form a correct idea of the moon's
mountains we must above all take into account the
size of that body. The irregularity of the fine of light
at the first quarter suggested to the ancient Greeks a
correct conception of the nature of the lunar surface,
but two measurements had to be determined before
there could be any proper appreciation of its mountains,
and this could not be done until centuries afterwards.

* We may also mention Neison 's Atlas, which is an elaboration of the Mappa
Helenographica, giving more of the rills but less details in the mountains, and
admitting many errors. There is a crowded map, 'La Lune,' by Gaudibert
and Flammarion, about 25 inches in diameter. This is a rather schematic
* carte pittoresque,' and shows a number of rills. It contains 509 names, and
costs about five shillings. There is also a map in Elger's, ' The Moon,' about
18 inches in diameter, and very clear. [Madler's map is reproduced in Webb'*
, ' Celestial Objects for common telescopes.' ]

52 THE MOON

The ancients succeeded in making a fair estimate of
the moon's distance from the earth' and of its diameter,
by determining certain lines and angles between the
stars. Aristarchus, of Samos (320-250 B.C.), found in
this way that the distance of our satellite was 56 semi-
diameters of the earth, and gave it a diameter of 2°,
which is excessive. We now know that the figures
are 60*27 semi-diameters and 0*52°. It has been
said that Aristarchus was more successful in his
difficult method of determining the distance than many
in the easier method of measuring the angle between
the horns of the crescent moon. As a matter of fact,
he was quite ignorant how large the semi-diameter of
the earth was in ordinary terms of measurement, so
that his 56 semi-diameters only give a proportionate
not an absolute, size. The insecurity of calculations at
that time can be seen in the results of Eratosthenes,
who allowed only 25 earth-radii. On the other hand
Hipparchus (190-120) came closer to the truth with
a distance of 59 radii and a diameter of 31'. But this
again merely means the proportion to the unknown
size of the earth, so that Hipparchus could only give
a proportional estimate of the real size of the moon.
Ptolemaeus (100-170 A.D.), again made the angle
much too wide. Since the application of the telescope
to lunar purposes, and since the insertion of a spider's
thread in the lens to fix a definite point, and the use
of carefully graduated instruments to determine small
angles, students have approached nearer and nearer
to the real size, and we now know that the moon
revolves round us at a distance of 60*274 earth-radii
(238,000 miles) and has a diameter of 31 '1' (minutes
of an arc), or 2170 miles. According to L. Struve,
the diameter, as determined by 42 stellar occultations
in 1884, on the basis of the Hansen parallax (57' 2'27")
is 31 ' 5*29"; and according to J. Peters it is, as
deduced from eight occultations of the Pleiades from

THE MOON 53

1840 to 1876, 31' 5 • IS 7 '. These determinations give the
moon a diameter of 2162 '4 and 2162 miles respectively.
In this way we can give a positive value to all our
arc-measurements and to parts of the lunar disk. If
we imagine an equatorial line drawn round the moon,
one degree of it must have a length of 19 miles, and
must be seen from the earth at an angle of 16 *6"
(seconds of an arc). Thus we get direct measurements
of the true diameters of the circular ramparts on the
moon ; only we must remember that nearly all circular
structures are fore-shortened when near the moon's
edge, and we must therefore always measure the
longer axis of the apparent ellipse.

It is a more difficult matter to determine the
height of the lunar mountains. It is true that, as the
pictures of the moon show, they cast deep black
shadows, long drawn out in some circumstances,
toward the night-side of the moon ; but these must
always be parallel to the equator, and their real length
only tallies with the apparent one when they he quite
close to the middle of the disk. As the terminator
(or line of illumination) is, like the parallels of longitude,
more and more bent towards the east and west, in
the higher latitudes the linear distances of an object
will be smaller and smaller as compared with the
angular distances expressed in their degrees of longitude,
and towards the east and west the shadows must be
optically fore-shortened on account of the rotundity
of the moon. It is therefore necessary to bring the
immediate findings of shadow-lengths, as determined
by the micrometer in the telescope, into proper relation
to their distance from the centre of the disk, before it
will be possible to establish their real proportion to
the moon's diameter and so express their length in
miles. Even then we have not yet got the height of
the mountain that is being studied ; but the first
measurement will give the height of the sun above the

54 THE MOON

mountain, and then we have only to find out what
vertical height will correspond to the said height of
the sun and the given shadow-length, and we have the
latitude of the mountain. We need only say here
that the results are more accurate in proportion to
the smoothness of the floor of the moon below the
point of the shadow, and the longer the latter is drawn
out. On the real moon, as a matter of fact, the
shadows are much deeper and sharper than on the
pictures of it. Hevel established long ago, with poor
instruments that only magnified from 30 to 40 times,
the height of a lunar mountain of 17,333 feet, and
there are much higher ones. Schroeter gave very
reliable measurements of many others. Madler deter-
mined the heights of more than 1,000, andrSchmidt made
altogether 3,050 measurements. We may say con-
fidently of many of these determinations that they are
much more accurate than most of the measurements
of terrestrial mountains outside of Europe. Indeed
Madler 5 s map was far more correct as a reproduction
of the moon than any map of the earth was, even at
the beginning of the twentieth century. The interior
of Africa, of north and south America, Asia, and
Australia — to say nothing of the polar regions — is not
yet as well charted as the moon was in this 70 year
old map. The reason is that we can see the whole
moon at a glance, while the exploration of foreign
lands involves costly and wearisome expeditions and
innumerable dangers.

A closer measurement of lunar objects on the
photographic plates has been undertaken for many
reasons, but chiefly in order to secure new and better
maps. An older theory assured us that the moon
departed a little from a perfectly globular form, and
presented to the earth an unusually flattish oval. Dr.
Mainka,* of Breslau, has made a large number of

* See his article in the * Mitteilungen der k. Univ.- Stern warte zu Breslau,'
I, pp. 53-71.

THE MOON 55

measurements in this connection. His results did
not establish the theory, but gave a number of inter-
esting suggestions of support, from which we could
infer the irregularity of the curved surface. These
determinations of level show at least that extensive
bulges and small swellings alternate with broad
depressions, and that the whitish mountainous regions
correspond pretty well to the plateau surfaces and
the plains to the depressions. The map shows this
very clearly.

Another peculiarity was discovered by Galilei in
studying the design of our neighbour-planet, and can
be seen with the naked eye at its greatest development.
This is a variation in the part of the moon comprised
in the disk, and is called ' libration ' from the Latin
libra (a balance). It is caused in the following way.
The moon's orbit is inclined to that of the earth at
an angle of 5° 8', so that it occasionally stands to
this extent north or south of the ecliptic. Moreover
the moon's axis is inclined a good 1° 5' towards it.
Hence, if the moon comes, so to speak, right above the
ecliptic, especially in the constellation Gemini, we can
see a good piece of its south polar region, and its centre
is a little north of the centre of the disk. Then, when
it lies quite to the south of the ecliptic, especially when
it is in the constellation Sagittarius, we can see a good
deal of its north polar region ; especially we who live
in the northern hemisphere and occupy a particularly
' elevated ' position in this respect. The two move-
ments together make up what we call ' libration ' in
virtue of which we see, alternately to north and south,
a crescent-shaped piece beyond the lunar poles.

We know further that the moon travels with
unequal speed in its elliptic orbit. It goes more quickly
when near the earth and more slowly when farther
away from it ; though it rotates on its axis with
perfect regularity. This causes another displacement

THE MOON

6, ^ ^> : ' ;
' .lit- , /;-.-'■ .; : (-2v-v X

Fig. 13.
Dr. Mainka's map, showing lunar levels.

of the moon's features, the lunar centre at one time
outstripping the orbital movement and at another
time lagging behind. Thus we get once more, alter-
nately to east and west, a crescent-shaped piece of the
other side of the sphere, which is generally invisible.

THE MOON 57

By frequent observation, therefore, we know, not
exactly half, but 0*59 of the moon's surface; the.
remaining 0*41 remains completely invisible. These
variations have, of course, been utilised by the photo-
grapher. Professor Franz has studied and reproduced
several plains in favourably situated positions, that
cannot be found on the older maps. Moreover, the
libration is the best means of combining pictures taken
at different times in the stereoscope so as to produce
an astonishing effect of plasticity.

Finally, we must mention certain standards that
should be within reach of every observer and that are
easily handled. These refer to the position of the
terminator in the lunar parallels of longitude. The
charts assign 0° to the centre, and count up to 90°
each way, eastwards and westwards ; they also give
the reverse, as seen in the astronomical telescope.
The illumination begins on the left edge of the chart
and proceeds as far as the right (full moon), then g03s
back from left to right. The lengths from the edge
(or limb) to the centre are progressively indicated by
the minus sign ( - ), corresponding to the fall in the
number of the degree ; the lengths from the centre to
the other limb are indicated by the plus sign ( + )
with progressive increase of the numeration. Thus,
- 32 6 means 32° left of the central meridian : + 17°
means 17° right of it. The latitude distances of objects
from the equator are indicated, as usual, as north,
(lower half of the map) and south (upper hemisphere).
There are tables that give the meridian of the ter-
minator for each day. We may give a few, with an
explanation, for the use of those who are interested, as it
is often necessary to know the limits of the visibility of
an object. In the present case we assume the year to
begin with March.

THE MOON

Position of the terminator each day between the
years 1906 and 1941.

1906

19-5°

1918

227-5°

1930

75-4°

March 1

6-1°

1907

249-9°

1919

97-8°

1931

305-8°

April 1

23-2°

1908

108-1°

1920

316.0°

1932

1640°

May 1

29-7°

1909

338-5°

1921

186-4°

1933

34-3°

June 1

48-3°

1910

208-8°

1922

56-8°

1934

264-7°

July 1

54-9°

1911

79-2°

1923

287-1°

1935

135-1°

August 1

73-8°

1912

297-4°

1924

145-3°

1936

353-3°

Sept. 1

92-4°

1313

167-8°

1925

15-7°

1937

223-6°

Oct. 1

98-4°

1914

38-1°

11926

246-1°

1938

940°

Nov. 1

1161°

1915

268-5°

,1927

116-5°

1939

324-4°

Dec. 1

121-1°

1916

126-7°

1928

334-6°

1940

182:6°

Jan. 1

138-1°

1917

3571°

1929

205-0°

1941

53-0°

Feb. 1

155-0°

(Progress of the terminator, 12 '15° per day;
0*51° per hour).

How to use it — From the meridian for the begin-
ning of the year (March 1st) the angle is to be deduced
that holds for the date — say July 16th, 1906. For
1906 we have 19 5° ; for the 1st of June 48 '3°, and
so for the 16th of June 15x12 '15°, or 182 "2° more,
or 230*5°. The latter figure is taken from the first,
19*5°, or from the meridian lengthened by 360°. We
thus get 149*0° meridian. The figures between 0° and
90° indicate western meridians (on the left side of the
map) of the morning terminator ; between 360° and
270° their difference from 360° indicates the eastern
position of the morning terminator ; between 270°
and 180° the excess over 180° indicates the western
meridian of the evening terminator ; between 180°
and 90° their difference from 180° indicates the
eastern meridian of the evening terminator. The
result given above, 149 *0° comes into this last category.
The difference from 180° is 31 *0°, and so the terminator
after midnight on June 16th, 1906, is at 31*0° eastern
meridian in the waning moon, and can only be con-
veniently observed about 2 — 3 o'clock in the morning.

CHAPTER II
Appearance and Reality

We have already mentioned the interesting fact
that even the ancients were acquainted with the
ruggedness of the moon's surface, as there are features
near its centre which cast long shadows, and these are
revealed by the irregularity of the line of illumination,
or terminator. It is clear that a mountain-chain,
stretching from the south-east toward the north-west,
with a steep fall on the side that faces the sun, must
cast long shadows toward the east (according to the
orientation of lunar maps) as the sun goes down. Its
eastern spurs will stand out prominently in the illu-
minated field long before the deeper-lying parts are
touched by the sun. Such a situation, with long and
broad shadows and illuminated peaks, is actually
found in the Apennine range (see illustration on
page 28), and was not unknown to the older astro-
nomers. But the conjecture can only be converted
into certainty by the use of optical instruments, and
we shall now see how they render us this great service.

Magnification of a thing by means of the telescope
is equivalent to bringing it nearer to us. Let us fix
a normal range of vision for things that we can hold
in our hand — say the letterpress of this book. We
may take it, for convenience, to be 10 inches. If we now
use a lens with a focal distance of 10 inches, we may

60 THE MOON

say that its images (received on oiled paper or a
ground-glass plate) seem to be in the normal range of
vision, and are not magnified, whether the object is
a landscape or a heavenly body. It follows that a
flattish lens, with focal image at 20 inches, must make
the object twice the original size ; and that with a spec-
tacle glass of 160 inches focal length the distant object
will be magnified 16 times, because the proportion of
160 to 10 is 16. Thus the glasses once made, especially
in Italy, with very great focal length, give of them-
selves, without any additional lens, a magnification of
30 or 40 or more times.

If we now use a short-focal lens, so that the image
to be examined lies behind the glass, we shall find
that its power of magnification is equal to the number
that we get on dividing the 10 inches by the inches of
its focal length. Thus if a lens has a focal length of
two inches, we have a power of magnifying 5 times.
Such a lens in combination with the above-mentioned
spectacle-glass (magnifying 16 times) would again
magnify the focal image (at a distance of 160 inches)
5 times ; so that the eye, looking through the lens,
would see the distant object magnified 80 times, or
brought 80 times nearer. The effect is therefore just
as if we were travelling toward the distant object —
toward the moon, for instance. If we take an opera-
glass that magnifies 2 times, and turn it on the moon,
the effect is the same as if it now came within 120,000
miles of us instead of 240,000. We may fancy that
we have lessened by one half the distance between us
and our satellite. A modern prismatic telescope with
a power of magnifying 5 times would bring the moon
within 48,000 miles ; a terrestrial telescope, mag-
nifying 20 times, will bring it to a distance of 12,000 ;
an astronomical telescope, with a power of 100, to a
distance of 2,400 ; and the workers with the very
large instruments can at times — this is the most, but

THE MOON 61

unfortunately, not the best, that art has yet done —
indulge in the luxury of a power of 4,000, and they
then see the moon at an apparent distance of 60 miles.

It must be remembered that when we make these
comfortable journeyings towards our distant planetary
neighbour, we really penetrate very far into the mys-
teries of its exterior. Those who have not themselves
enjoyed the experience, sometimes shake their heads
incredulously, and point out that this extreme approxi-
mation is impossible, and that Snowdon, for instance,
would make a very poor and hazy appearance at a
distance of 60 miles. It may be urged in reply that
Mont Blanc can be seen at a distance of 153 miles,
and the mountains of Corsica can be seen from Monte
Viso, a distance of 160 miles. Moreover, seeing things
in an horizontal direction, through the thickest and
least pure layers of the atmosphere, is a very different
thing from seeing things at an altitude. It is true
that the height of the atmosphere is considerable, but
it decreases rapidly in density, and therefore increases
in clearness.

We can illustrate the point with a few simple
figures. We have long known that at the sea-coast
there is an atmospheric pressure equal to the weight
of a 30 inch column of quick-silver. We also know
that we must ascend about eleven yards in order to
lessen the pressure by 25 th of an inch. It follows that
if the atmosphere were of equal density at all levels,
like a block of glass, we should only need to ascend
8,450 yards to reach the upper limit of it. Roughly
speaking, therefore, seeing things vertically through
the whole thickness of the atmosphere is almost
equivalent to seeing things horizontally at a distance
of five miles. We can thus understand how it is that
mountains at a distance of 20 or 40 miles look such a
watery blue, and are mere pale shades at a distance of
150 miles. But telescopic vision has not only the

62 THE MOON

advantage of showing non-terrestrial bodies with
comparatively little loss of light — taking into account
the purity of the upper atmosphere, as well — it is
much sharper in itself, and the limitation of the field
of vision, and possibly of the object, allows an extreme
concentration of one's attention on a small surface, so
that it can be profitably studied in its smaller features.

It is astonishing to what a depth we are thus able
to explore the lunar world. We can tell approximately
whether an object that has an apparent diameter of
only 2M th of an inch is round or oval, and the result is
very interesting. The author generally works with a
power of 200, and can therefore perceive things 200
times smaller than such an object. This would be
seen by the eye at a visual angle of 1J minutes of
arc ; hence, when it is magnified 200 times the size
need only be * 375" (seconds of arc) for us to have a fair
idea of its shape. But on the moon, in good conditions,
0*375" means only 644 yards. Hence, with even
moderate instruments and powers, hills of 640 yards
diameter can be seen on the moon !

We must remember, moreover, that the lunar
mountains sometimes cast gigantic shadows. A
mountain 2,200 yards high may cast a shadow 60 miles
long, and a hill only 22 yards high (as high as a four-
storied house) may have a shadow 1,100 yards long.

These are things, therefore, that, in favourable
conditions, fall within the range of my modest obser-
vatory at Landstuhl. I will only add for the moment
that a trained eye would be able to see, in the larger
telescopes, lunar structures of about the size of a
modern town school. In comparison with this the
detail that has been explored on the nearest planet,
Mars, since Schiaparelli's epochal discoveries, is very
scanty, as will be seen on an examination of the map
of Mars here given. The naked eye can perceive on
the moon at a distance of 240,000 miles, many thousand

THE MOON

Fig. 14
(t. V. Schiaparelli, director of the Milan Observatory.

times more than the finer details on the, tiny disk of Mars,
which is, at its nearest, 135 times as remote. Hence
if the surface forms of a distant world seem to be
described in the following pages with some facility, as
if it were a trifle to span the 240,000 miles that separate
it from us, the reader will now approach them with
confidence. Nothing is so unsatisfactory as having
to take everything on trust in unfamiliar matters ; and
nothing so much enhances our pleasant interest in
facts as a knowledge of the way in which they are
ascertained.

* In default of a direct examination of lunar scenery
by the telescope we must be content with the admirable
pictures which we owe to the faithful camera (compare
the picture of the Apennines, page 28). The hardness
of the landscape, which is due to the depth of the
shadows, will seem strange to us. We are accustomed
to see every stage of illumination in one and the same
object, from vivid light to deep shade ; absolute black

THE MOON

Fig. 15
Mars on June 5th, 1888 (central meridian = 300 c ) , by Schiaparelli.

alone is wanting, because the diffused light penetrates
into every corner and cleft. We speak of body-shadows,
that help us to realise the contour and depressions of
things, and of cast-shadows, which are more or less
dark patches, of the same outline as the body itself, on
the side away from the light. We do not find both
these kinds of shadows in the usual form on the moon.
The only shade beside the fully illuminated surface is a
half-light, due to oblique illumination. All the rest
is perfectly dark. There is practically no twilight.
On this account pictures of the moon have a singular
hardness and coldness of tone. We must further
remember that the light portions of the pictures are

THE MOON 65

not all as vivid, and the black not at all so intense,
as the real shades on the moon. * In the reality we
find dazzling light and inky darkness in hard contrast.
On the other hand there is an exaggeration of the
moon's plastic features. These have to be raised to
such a high scale to give their real size, that we need
figures and illustrations to help us to form a correct
idea of the structure of the, lunar mountains. The
dominant forms look like the mouths of craters, or
at least like deep cauldrons with very prominent walls.
The first observers embodied this impression in their
phrases, and so we still convey wrong ideas in the
names we give these structures. The circular forms
on the moon are not mouths, or cauldrons, nor even
depressions of a disk-like character. When we do find
considerable depressions, it is amongst the smallest
structures that our pictures reproduce. Even the
hollow of a flattish dessert-dish would convey an
exaggerated idea of the character of the large and
medium-sized circular structures on our satellite. To
realise the difference between the popular notion and
the real lunar landscape, we may take an instructive
experiment of Nasmyth's and a few figures.

Fig.16
The shadow of a split pea in a strong light.

Nasmyth photographed the shadow cast by a
split-pea in a very strong light, and found it was six
times the length of the pea's diameter. It is possible
to make the shadow 20 times as long, or even more ;
so that we cannot take the length of a shadow as an
absolute indication of the size of a body. In the same

66 THE MOON

way the shadow seems only to fill the mouth of a lunar
' crater.' As a matter of fact the ' mouth ' is in many
cases so incredibly shallow that the eye of an observer
on the crest would hardly be able to see the crest on
the opposite side, because the depression is so slight
that the curvature of the moon's surface covers the
opposite wall. We must support this very curious fact
by some figures and an illustration. One of the
largest cavities (called Clavius) has a diameter of about

Clavius. S: 230 km

Plolem&uLS^2,i 185 k?n ..
Pla.lo, 2 : 100km. ^^^v***^ 7hru,ntius, <f* 70k*».

*7ope rrv i otcs. 3.3 : 90 km . 4rcA un <°oW, j?> . SO A»*t>

Fig. 17
Profiles of several craters in their real proportions.

142 miles, while the wall has a peak (this is not the
average height of the crest) to the west of a little over
three miles (17,300 feet) ; on the east the altitude is
generally greater than on the opposite side, also
reaching more than three miles. Thus the proportion
of height to diameter is 3 : 142, or about 2 per cent.
Another so-called ' depression ' (Ptolemaeus) measures
115 miles, and rises to a height of 8,600 feet on the
west and 4,000 feet on the east. In this case the
proportion of height to diameter is 0*65 per cent. A third
structure (Plato) is 62 miles in diameter, and rises to a
height of 6,700 to 7,500 ft. in the peaks ; its proportion
is 2 per cent. A fourth (Copernicus) is 56 miles in
diameter, and has peaks of 11.000 ft. : a percentage of

THE MOON 67

3*66. Archimedes, a fifth, is 50 miles in diameter, and
rises to an average height of 5,700 ft. : percentage 2*1.
Finally, a sixth 'crater' (Taruntius) is 43 miles wide and
has a western height of 3,300 ft. : percentage 1*4. A
dessert dish five inches in diameter (without the border)
and less than a quarter of an inch in depth has twice as
deep a cavity, proportionately, as the deepest of these
depressions.

The slopes are in proportion to this very slight
absolute depth. Julius Schmidt made a study of these
lunar features, and he tells us that ' there are very
rarely acclivities of 60° or over ; and they are in such
cases confined to small stretches (that is to say, the
highest crests). We find inclinations of 25° to 45° very
frequently. Most of the craters have falls of 3°-8° on
their outer faces, and 25°-50° internally. Isolated
mountains, such as Pico and many similar ones, are
about as steep as terrestrial volcanoes, but frequently
enough they are less steep. There are no vertical
precipices or crater- walls on the moon.'

The present writer has made a systematic investiga-
tion on this point, and has reached the following results.
As Schmidt's conclusions were described by the great
English selenologist in 1881 as very acceptable — he
himself holding that ' an average inclination for the
inner wall of 8-12° towards the foot and 15-25° near
the peak seems to be the most correct expression ' —
the author determined to carry out some extensive
observations in order to secure more reliable data*.
In the course of several months 1065 measurements
were made with the telescope, and when these were
arranged and worked up they gave the details of 687
ring-structures. The classification of the angles of
inclination discovered in the inner steeper walls of
these structures gave an angle of over 17*5° in 112

* See the author's article in the Axtronomische Nachrichten, no. 3266.

68 THE MOON

cases, a little over 22*25° in 290 cases, just 23*5° in
256 cases, and a little less than 23*75° in 16 cases.
In the rest (13 cases) the measurements were ordinary.
In any case it can no longer be doubted that the
average inclination of the interior walls of lunar ring-
mountains — reckoned from the crest to the foot — is
only 22 — 23°, a figure that will be found in our own
terrestrial mountains. There are, of course, both on
the moon and on the earth, conspicuous departures
from this average, hence it was worth finding out, also,
what is the proportion of the size of a ring formation
to its depth, or to the steepness of its slopes. It was
long known, from direct observation, that large rings
have rather easy slopes, but there were no accurate
figures. From the author's work, in relation to the
diameter of the ring-mountains, the following results
were obtained. Of the objects measured, those up to
6 miles in diameter had an inclination of 33* 1° ; those
up to 12J miles, an inclination of 34 * 2° ; those up to
18 miles, an inclination of 33*8° ; up to 25 miles, an
inclination of 21*4° ; up to 24 miles, an inclination of
15*5° ; up to 60 miles, an inclination of 14*2° ; and
the largest (over 60 miles) an average inclination of
11 * 6°. The relation of the first three groups is striking
and it is permissible to give ring-mountains up to 18
miles in diameter an average inclination of 33*5°.
The two following groups also may be combined, and
we may say that the walled rings of 18-30 miles
diameter have an inner slope of 22*7°. The next two
groups — diameter of 30-60 miles — have an inclination
of 14*8° ; and the group of the largest walled plains
is distinguished for the least inclination of the inner
walls, about 11*6°. We have thus not only a statis-
tical confirmation of the appearance, but also a striking
graduation in the relation of size and steepness, which
should be carefully taken into account by those who
would frame theories of the moon.

THE MOON

In connection with these investigations, a third
was undertaken, with the object of distributing the
lunar ring-structures according to their size. It could
be seen at a glance that the largest structures were the
flattest ; they also seemed to have the gentlest
slopes, and the above figures confirmed this ; and,
finally, they were the least numerous. There is an
immense number of the smaller crater-forms. The
question was, whether we could get statistics on this
point also, showing, as in the case of inclinations, that
there was a certain affinity between forms with like
dimensions. The monotonous work of measuring was
conducted in regard to 2,154 forms, and, after a good
deal of classification, gave something like that result.
From the first it was neither intended nor necessary
to include the smallest rings ( ' craters ' ), which
run into tens of thousands. The author set to work on
those forms which measure about 3 miles across, and
studied about 700 of them, as the following table
shows : —

Diam.

miles
3

15J

Number

700

630

268

144

Diam.

42J

Number

33 i 24

There are in all only 26 walled plains with a dia-
meter of more than 62 miles. The absolute number of
crater-like forms on the visible hemisphere of the moon
increases very rapidly with the smallest ; from 15
miles upwards the decrease in number is steady and
constant. The variations in this last part of the curve
are scientifically insignificant, but the transition from

70 THE MOON

high figures to low ones is very significant. Something
remains to be discovered here, as the matter cannot
be due to chance. If meteoric impacts had been, as
many suppose, the cause of the engendering of
these features, there must have been falls of meteors
on a colossal scale. Where are they to-day ? On the
other hand, if they were due to volcanic action, this
must have needed thousands of vents for the play of
its forces. Thus the statistics seem to confirm the
selenological theory hereafter advanced.

According to what we said previously, we should
have a convenient and very instructive means of
exploring the moon by reducing its distance from
us by a half, a quarter, a tenth, or a hundredth,
according as we use an opera-glass or a terrestrial
or astronomical telescope. We must leave this
enjoyable pursuit to those who possess the instru-
ments, and turn to our pictures and maps, and
examine the results of a hundred years' industrious
observation of our satellite. The reader who wishes
to learn the smaller features of its topography from
maps and manuals, as we do in terrestrial geography,
will find in Neison's work plenty of description and
illustrations*. But for our present purpose we shall
in our inquiries into the nature of the moon, and the
peculiarities of its surface, prefer dry statistics to the
examination of pictures and speculation on features
that differ so widely from those of our earth.

At our first sight of the moon the eye sweeps over
its surface and gets a general view of numbers of
similar structures. We involuntarily select a few of
these, so that the eye may fix its gaze and examine
them more closely ; for the warty face of the moon
seems to be sown with large and small rings. They
seem to be circular in and about the centre of the disk,

* * The Moon, and the condition and configuration of its surface,' with an
t atlas* of 726 maps, and 5 coloured plates, 1876.

THE MOON 71

but elliptical toward the limb, and their axis becomes
shorter as they approach the edge of the disk. Com-
pared with this ubiquity of the ring-forms, the elevated
structures that we call mountains, on the analogy of
terrestrial objects, are small in number, though of
considerable height. The number of the round struc-
tures gives the unaccustomed eye of the layman the
impression of an almost inextricable confusion of
forms, so crowded together that they have to encroach
on each other's space. There are a good many of these
clusters and chains ; and when the eye is a little
accustomed to the sight, new and smaller craters come
into the field of vision, so that in some places the floor
of the moon seems to be perforated like a sieve. If
there were not extensive and well-defined plains, and
if the shoals of smaller rings did not cling like parasites
to larger objects, so that we can eventually group our
impressions, in spite of the confusing number and
irregularity, we should doubt whether we could succeed
in drawing up a good map of the innumerable wrinkles,
holes, veins, and mountains. Our illustrations give
only a feeble impression of the real aspect of the moon,
because the much-reduced reproductions of photo-
graphs only include ' craters ' of at least nine miles in
diameter. And we need only glance at these pictures
to realise that we have nothing on our earth to compare
with such structures. In the true sense of the word,
the moon is a foreign world.

The mountain-forming forces that created our own
heights and crumpled the earth's external crust are not
revealed in the corresponding mountains of the moon,
quite apart from the rings. There is practically
nothing analogous to them in our planet, especially if
we consider their structure and their finer features ;
there is nothing like these on the earth. The first
impression is very deceptive, and it is quite natural
to take the name ' crater ' in the terrestrial sense, as

72 THE MOON

the mouth of a volcano ; particularly as in many cases
there is a central elevation within the surrounding
walls, and this is a common feature of terrestrial
craters. As long as people had only vague ideas of
the real extent and the plastic features of these ring-
elevations the name of ' crater ' could very well be
retained. To-day, it ought to be at least used with
reserve as a mere expression of general form, because
on closer investigation there is as much difference as
possible between terrestrial and lunar craters. (Com-
pare the profiles of the two).

In order to identify one's position in repeated
observation of the chaos of lunar details, and to explain
one's discoveries to other observers, the practice came
in with the invention of the telescope, of giving names
to the chief structures. Between 1620 and 1640
Langrenus introduced the names of famous men into
his map. But as his work was forgotten, Hevel of
Danzig invented new names, taking a certain resem-
blance between the mountains of the earth and those of
the moon as his base, and transferring our geographical
terms to our satellite. Hardly four years had elapsed
since the publication of his work (1651) when Riccioli
of Bologna published a map. He returned to the plan
of Langrenus, and again gave the names of distinguished
astronomers and mathematicians to the spots on the
moon. He left Hevel' s title of ' seas ' however, to
the lunar plains, though he gave them names to indicate
the various astrological influences that were supposed
to emanate from the moon. But his substitution of
' terrae ' for the names of the mountains was not
maintained, and Hevel' s geographical names (Alps,
Apennines, etc.), have survived. It is clear that the
early selenographers, with their imperfect instruments,
did not penetrate very deeply into the mysteries of
the outer crust of our satellite, and the names they
gave were satisfactory in the then state of knowledge.

THE MOON 73

With the improvement of the telescope and the
enlargement of our knowledge of details, it became
necessary to form a new nomenclature. Schroeter
had to extend the list, and Beer and Madler introduced
150 new names — names of scientists for the ring-
structures, and of terrestrial mountains for the new
ones on the moon. They had also to develop Schroe-
ter' s other innovation, which consisted in giving the
name of a large structure, together with a distinctive
letter, to smaller forms in its vicinity. In this way
a very extensive orientation became possible ; simple
elevations were indicated by Greek letters, depressions
and craters by Latin ones. Capital letters notify that
the object so named is a point of measurement. Later
on a committee of the British Association, which
dissolved after a brief activity, thirty years ago,
contemplated the introduction of a new system,
which was impracticable, but certainly would have
allowed the classification of an immense amount of
detail. The moon was to be divided into four quad-
rants, each quadrant into 16 sections, and each section
into 25 special surfaces. The sections would have
Latin, the surfaces Greek letters ; and each object in
the latter would be designated by a number. Thus, when
a small crater was called I A o 16, it would mean object
16 in surface o (omicron) of section A in the first quad-
rant. It was intended to have a map of the moon
100 inches in diameter, on which the surfaces would
be squares 2 inches in length. A similar plan of divid-
ing the map of the moon has been mooted lately.
However, English and other observers have continued
to introduce new names on the old system, whenever
it was necessary, and it is retained in Schmidt's large
map.

It was necessary to have some unity in nomen-
clature, but it is certainly not necessary to have a
rigid classification. We have already pointed out

74 THE MOON

that the names that were given to the large and small
ring-structures were mere descriptions of their form,
and conveyed no idea of their real nature. When we
hear a terrestrial structure called a ' mountain-cone '
we have some idea of its shape. If it is called a
' volcano/ we do not of course associate it with a cone-
shape, but we chiefly think of it as a special geological
form of mountain, with a very distinctive origin and
development. It is quite otherwise on the moon.
In its case, seeing that we look at everything from a
respectable distance, we cannot at once pronounce on
the nature of things, but can merely say what they
look like in a general way. Any layman who is able
to appreciate size from the distribution of light and
shade will at once describe a number of lunar forms
as holes, mouths, peaks, etc. If in addition to his
knowledge of them as depressions lying between some
sort of walls, he is also aware that they are extra-
ordinarily flat, he will not only describe them as
depressions, cavities, dishes, flat dishes, and so on, but
will seem to have aright to attribute definite characters
to them. As we have mentioned several times that
the word ' crater ' very early came into use in seleno-
graphy, and is still retained in it, we must now see
how far the name is justified. We know from what
we have already seen that it is, unfortunately, not an
appropriate description of the lunar mountains. It
was a hasty designation of them on the ground of
their purely superficial features, and those who be-
stowed it were not sufficiently on their guard against
deceptive appearances. Those who use the word
4 crater ' to-day must remember that it is merely a
superficial description of an external form.

Following Neison's classification,* we will now
distinguish between a number of lunar structures that

* ' The Moon,' ch. III.

THE MOON 75

have a certain resemblance. The entire visible surface
of the moon may be distributed into three great classes,
plains, craters, and mountains ; the term craters being
used only in its usual conventional sense. The first
class, which occupies more than half of the entire lunar
surface, is divisible into the two great sub-classes of
dark and light plains. The first includes the lunar
Maria with the smaller formations to which the terms
Palus, Lacus, and Sinus have been applied ; whilst the
formations comprised in the latter class have received
no distinct name, and seldom possess as definite borders
as the former. Under the single term craters, in
compliance with the conventional usage of the name,
have been grouped the whole mass of the formations
of the moon, which, when perceived with a low power
and a small aperture, are supposed to bear some
resemblance in appearance to the volcanic craters,
though they are of the most diverse nature, and mostly
without the slightest claim to be regarded as such.
These formations will be divided into nine classes,
namely, walled-plains, mountain-rings, ring-plains,
crater-plains, craters, craterlets, crater-pits, crater-cones,
and depressions; each of which possess distinctive
features, though the lines of demarcation are of necessity
somewhat arbitrary. Finally, the mountain-formations
may also conveniently be separated into twelve classes,
namely, the great ranges, highlands, mountains, and
peaks, constituting the greater elevations ; and hill
lands, plateaus, hills, and mountain ridges, forming the
lesser elevations, whilst the numerous small irregu-
larities of the surface are comprised in the four divisions
of hillocks, mounds, ridges, and land-swells.

Neison's scale of names, taken together with the
remark about ' craters,' almost agrees with the principle
of Dugald Stewart : ' Phenomena should always be
described by names that involve no theory as to their
causes. These are the subject of separate investigation

THE MOON

and are best understood when the facts are considered
impartially and independently of anything that must
be regarded as unknown. This rule is particularly
important when the facts are complicated to some
extent.' This maxim* (which Madler took as his motto
at the beginning of his chapter on ' Topography,' etc.)
has not always been borne in- mind ; especially in
regard to the ' lunar craters,' which were already
considered to be volcanoes when people knew hardly
anything about them except their roundness, and in
regard to the ' canals on Mars.' It is true that there
are certain slender lines and streaks of shade on Mars
that give rise to the latter designation, but they can

Fig. 18
Mars on June 12, 1888 (central meridian = 240°) by Schiaparelli.

THE MOON 77

only be regarded as ' canals ' in our sense of the word
by assuming a great many other conditions. Even
Neison himself fell into a certain play with words, as
we see in the expressions ' crater,' ' crater-elevation,'
' crater-pit,' ' small hill,' ' ridge,' and ' hillock.' If we
avoid dogmatic ideas of real selenological value until
we are in a position to give a proper explanation of
all lunar forms, we may, with some convenience, apply
phrases taken from terrestrial geography to our
satellite.

CHAPTER III

Light and Colour

One can see at a glance in pictures of the moon
the apparent extent of the ' plains ' on this side of
its surface. They are distinguished by their darker
tone and less variety of form, though this is com-
pensated by the considerable graduation of light
and colour on their surfaces. Neison's observation,
that they comprise more than half of this hemisphere
of the moon, must not be misunderstood. We see the
parts of the moon that he towards its limb very much
fore-shortened, because they are on a round surface.
It is at all events true that the area of the gray plains,
as measured on a map or photograph, covers 0*4 of
the disk, but rather less than this in reality for the
whole lunar globe. In this point, therefore, there is
again no analogy between the earth and the moon, as
the terrestrial oceans make up about * 7 of the entire
surface. Further, the oceans form the far greater part
of our southern hemisphere, whereas the relation of
depressions to elevations in the moon is quite different,
the plains lying more northward and near to the
equator. And, as regards the total proportion of lunar
plains to the higher land, we must remember that
we know nothing about the distribution of mountain
and level plains on the other side of the moon.

THE MOON 79

These level plains, as yet little explored and very-
poor in detail, have been called ' seas,' though there
is no ground for the name. It has stuck to them,
however, as the map of the earth afforded a very
deceptive analogy, and especially as the state of things
seen on the moon in astronomical telescopes was
supposed to show a similar distribution of heights and
depths. But even our best optical appliances can
discover no trace whatever of water, or the action of
water. It is true that Chacornac (quoted in Neison)
believed his powerful instrument revealed, on a close
investigation of the moon's structure, much greater
analogies with the earth than were generally admitted.
Sir J. Herschel thought he discovered many traces of
the former presence of water, such as the formation of
diluvial deposits ; and Professor Phillips* indicated
several analogies between volcanic structures on the
earth and on the moon and found many proofs of the
action of a destructive atmosphere. We will only
observe that these three astronomers cannot be
regarded as authorities on the moon, because there
are no results of any importance whatever in the
science that we owe to them ; in their case the wish
seems to have been father to the discovery. If any-
where, the moon is the place for a man to discover
whatever he wishes ; and we must remember that in
their time it was very little known.

The plains are characterised by all the geographical
features that distinguish large terrestrial depressions,
but they have not the same geological features. On
our earth the water and atmosphere have mechanically
and chemically softened the hard features of its
earlier physiognomy and helped to level it. Generally
speaking, the lunar plains, with their variations of
colour and their bands of light, are seen under good

* 'Notices of some parts of the surface of the moon,' 1868, with
five illustrations.

80 THE MOON

illumination to be very much dinted, veined, granu-
lated, and even torn. In many places isolated peaks
and hills rise abruptly from. the surface, without any
gentle slopes at 'the foot ; there are even small plateaux
rising from the'flat ground, and an incalculable number
of large and small ring-structures are scattered over
it. Taking them as a whole, these level plains follow
the curvature of the moon, but there seem to be
round protuberances of almost imperceptible slope and
base-line, and flat depressions with indefinable ' shores,'
that can only be perceived when the sun passes directly
over them. These marks of slight inequality should be
carefully explored, and can only be studied by one
who' is practised in lunar observation, because they
do not cast shadows. The author is acquainted with
some cases where flattish eminences lie much like
thin disks on the floor of the moon. They generally
have a little ' crater ' inside them.

It is extremely interesting to study the borders
of the large ' seas.' Especially round the Mare
serenitatis*, very clearly on the coast of the Mare
nectaris, and to the experienced eye just as clearly on
the south-west and west borders of the great Mare
imbrium — we have already seen the meaning of these
curious names — we can perceive lines of cleavage in
the plains running parallel to the coasts in wide circles.
This points to a repeated sinking inwards, with a
secondary action toward the chief coast. The same
traces will be found by those who can read lunar
photographs in the isolated depressions of the Mare
crisium and the Mare humorum. They are not,
however, a peculiarity of the plains ; there is quite a
number of large ring-mountains or crater-plains with
the same characteristics in their much smaller interior.

*If the reader has not a special map he should consult the map in one of the
large atlases or in an encyclopaedia. For about six shillings one can get a very
full general map by Flammarion-Gaudibert, with 509 names.

Fig. 19
The ring-plain Gassendi and Mare humorum with concentric rills and
mountainous veins (1 mm. = 3700 m.)

82 THE MOON

In order to show the affinity there may be between
the largest and smallest of isolated circular depressions
on the moon, we will give a few names with the res-
pective diameters : Mare imbrium, 750 miles ; Mare
serenitatis, 437 ; Mare crisium, 312 ; Mare humorum,
270 ; Mare nectaris, 187 ; ring-plain Petavius, 90 ;
Posidonius, 69 ; Cyrillus, 56 ; Gassendi, 55 ; ring-
mountain Taruntius, 43 ; Doppelmayer, 42 ; crater
Lambert, 17 ; small parasitic crater Hesiodus, A 10 ;
small crater Ramsden, 4 miles. All fourteen have the
same features and lines of cleavage on the inner edge
of their cavities, though these secondary phenomena,
the outcome of a process that no expert has yet ex-
plained, have assumed the shape of concentric inner
craters in the three smallest structures. Finally, it
is only one step from these objects to the ring-plains
and ring-mountains with finely formed terraces on
the interior walls. We could again quote specimens
of this type amongst objects of very different size — a
further indication that selenology will have to include
all the ring-formations, even the largest, in one general
explanation.

Fig. 20-26
Shadows cast by peaks ; a. Archimedes, north : b. Archimedes, south :
c. Pytheas, east : d. mountain on the rill of Hyginus : e. e Pico B : /. Cauchy,
east.

Whenever we find a mountain rising abruptly
from the level on our earth, it either is or once was
a volcano. Take, for example, Vesuvius, or Kilima

THE MOON 83

Ndscharo, or Ararat. At the same time it always
has some foreground with a gentle slope. It is only
in a situation like that of Stromboli, which has its
base at a great depth of the sea, or of the eruptive cone
in the crater of the isle of Santorin, that we find a
well-marked obtuse angle between the surface of the
sea and the sides, or, in other words, a hard contour
in section. There are plenty of these abrupt cones
and hills on the plains of the lunar ' seas,' and they
are just as devoid of ' foot ' as Stromboli. This is
not merely one species of structure there, but the
general rule ; to such an extent that it is quite excep-
tional to find a hill of a different character. This is
very striking and remarkable, and it is quite clear that
the forces that have been at work on earth levelling
the heights and curving the slopes have not acted in
the moon. These agencies are water and the atmos-
phere, denudation and weathering. We cannot, there-
fore, assume when we see mountains ' sunk ' in the
plain, so to say, as well as ring-walls and ' craters,'
that their feet are buried in diluvial deposits, because
it would be a serious question where the material of
the deposit came from. For this divergence between
terrestrial and lunar phenomena there seems to be only
one explanation, and we shall indicate this at a later
stage.

The close relationship of the plains and the ring-
formations is seen in their circular borders, their
comparative or complete isolation, and the charac-
teristic parallel lines near their edges. We might
almost put it that the constructive agencies produced
large, medium-sized, small, or very small circular
forms, according to the intensity and duration of their
action ; taking into account, of course, the quality of
different parts of the lunar crust in advancing or
retarding the work. In this respect we may very well
introduce the meteoric influences suggested by W. and

84 THE MOON

A. Thiersch, at least in the sense that meteors may
here and there have initiated the formation by their
impact and, possibly, perforation of the crust ; just
as the flow of resin is started by boring a hole in the
tree. In the same way the strain of the pressure on
some material underneath the crust may cause it to
work out, and this may depend on lunar conditions
that have nothing further in common with volcanoes
than the fact that it is an eruption from within—
probably the only direction in which lunar forces can
expend themselves.

However, that may be, there is certainly an affinity
between plains and ' craters ' ; though the former
are large enough to comprise in their area all the other
peculiarities of the moon's surface. We find perfectly
formed and rudimentary craters of all sizes, the purest
specimens of the species being alongside ruins, plateaux,
irregular masses of hill, precipices, wart-like or boil-
like growths, long veins with a flat profile, and cracks.
When the sun rises or sets over some parts of the
' plain,' it often looks as if the floor of the sea had a
granular roughness, and this, in consequence of the
innumerable minute shadows, gives it a dark appear-
ance. In other places the smooth floor can be so
clearly seen in a strong light that it is possible to pick
out its finest features and distinguish the smallest
elevations. In these cases it is especially advan-
tageous if the ground is of a light colour in itself.

The mention of colour brings us to a fresh feature
of the sunlit face of the moon. It is, of course, difficult
to distinguish colour clearly in a field where one shade of
light blends with another so closely, and it will generally
be missed by an eye of little experience, on account
of the flood of light that enters the pupil from a large
telescope. Beyond an impression of yellow, white,
and gray, shading into black, inexperienced observers
can see no colour at all. But when one has learned,.

86 THE MOON

for instance, to compare certain localities of a bluish-
green or yellowish-green with others, it is possible
to recognise delicate shades even in a strong light.
The naked eye can hardly see any difference in the
intensity of the light on the illumined surface at
the first quarter, full moon and last quarter, but we
can see it in the telescope. The brilliancy increases
and decreases almost with the progress of the phases
of the moon.

At first one is inclined to ascribe the greatest
brilliancy to the full moon, and to regard it as equal
in the two quarters — apart from an inequality between
the brighter mountains and the gray plains, which is
included in the calculation. In reality it is somewhat
different. The material composing the external shell
of the moon has a peculiar property, that may be
briefly defined as a bleaching under the rays of the
sun. The elevated masses emerge almost gray and
dull out of the 14 days long night into a day of equal
length, and their creamy yellow changes into an almost
pure white — at certain spots, at all events — and then
loses its tone again as the sun passes away. The
influence of the direct rays requires some time to
produce the brightest tone, — and so it happens that
the bleaching process does not reach its height at the
beginning of full moon, but one or two days later.
Then there is a very remarkable colouring of the disk
towards the west, but the brighter rest of the moon
only gradually loses its brilliancy. The lingering of
the strong light thus causes the last quarter to be
brighter than the first, in which the bleaching is only
beginning. It takes some time for the bleached parts
to lose all their light again, as we see in the maintenance
of the brilliancy of crater-edges. If other round
cosmic bodies consist of the same or similar material
at their surfaces, and so exhibit similar retardations
in the process of illumination, it will be impossible to

THE MOON 87

determine their illumination by a simple formula for
each phase ; there will always be a difference that the
formula does not cover. Astronomers have experienced
this in the case of many bodies, and so each law has
come to have its ' anomalies. 5 Nature does not proceed
according to pure formulae.

We have already pointed out- that all the colours
do not attain equal brilliancy, hence it is that we see
a ' man,' a ' face,' or a ' kiss,' in the full moon. We
might say that the disposition to bleaching is fairly
even among the different tones in the moon's surface,
with the exception of certain blackish and whitish
parts, which do not become very bright on the one
hand, or increase in brilliancy almost to a pure white
on the other, and would give us very much more
contrast in the full moon if the deep shadows had not
disappeared. The meaning of the full moon is that
we are looking at our satellite almost parallel with the
sun's rays, so that it is impossible for it to cast any
shadows ; we see it under a vertical sun. All that
formerly looked warty and rough is now smooth and
without relief. If it were not for the half-tones and
brilliant points and mountain-ridges that remain, it
would be impossible even for the expert to identify
regions in the full moon ; and the difficulty is still
further increased by the appearance of bright bands
and spots of light that have, as a rule, nothing to do
with the moon's relief. To look for the map-details
on the full moon is like looking for a needle in a load
of hay. We find the same confusion of light lines and
thousands of spots on the new moon, that is to say,
at the phase in which the moon is invisible except
for a few seconds during a total eclipse of the sun.
But although the new moon phase is almost useless
for telescopic investigation, the small crescents just
before and after new moon afford an interesting
glimpse of the condition of the ' dark ' part. If we

88 THE MOON

examine it with a low power on these occasions we
find that the night-side of the moon has, generally
speaking, the same features as the full phase. By
choosing favourable periods — for instance, the spring
for the waxing, and the autumn for the waning moon —
periods when the narrow crescent is best placed as
regards twilight and the vapour line of the atmosphere
very minute features can be observed on it. The
light is, however, exceedingly delicate, as it is merely
the light reflected on the moon from the earth, bringing
the night-side within the range of visibility for the
naked eye. Many a reader will have seen the ' new
moon in the old moon's arms,' as popular phraseology
puts it. It may be noticed that the waxing moon is
a little less bright than the waning crescent. The
reason of this is that in the one case it is the western
hemisphere, with America and a great expanse of
ocean, in the latter the eastern hemisphere, with Asia
and Africa and less ocean, that reflects the sunlight on
to the moon. Our satellite therefore has its earth-shine
just as we get moonshine.

Chief amongst the features that strike the observer
of the full moon are the rays of light. Here selenology
has still a problem to face, and all its finest combina-
tions have broken down before the phenomenon of the
bundles of rays or lines that stream out from certain
very brilliant ring-mountains. It is a pity that the
observers who believe they have made themselves ac-
quainted with these enigmatic systems of rays have
allowed themselves to be hypnotised by the purely
external feature of the radial position of the lines, just
as they stopped at the circular form of most of the ele-
vations and at once pronounced them ' craters.' What
is called a ray or streak of light is not one continuous
object when seen in the telescope, but the effect of an
accumulation of spots and lines — dots and dashes — of
light. It is the arrangement of these in a longitudinal

THE MOON 89

direction and their concentration on the region of a
ring-mountain that gives rise to the appearance of a
' system of rays.' Refraining from any speculation as
to how these pencil marks may have arisen on the rough
surface of the moon, our first task will be to determine
the nature, connection, and extent of the various con-
stituents of the radiating crown. It is possible that
here again a mass of detail will give a clearer idea than
the broad impression made by an entire system.

From pictures of the moon at advanced phases
and from observation we know that the rays have a cer-
tain breadth and extend over enormous regions. Hardly
has the sun passed over these particular districts than
the first trace of the brighter streaks appears on the
illuminated surface. The structure, therefore, is already
there, and is generally clearly recognisable in the earth-
shine of the new moon at the times we have stated. As
the sun advances, or as the radiation of the sun increases,
a streak of light is defined more and more against the
different tones of the lunar floor, and finally shines
almost a pure white, remaining visible, and paling but
little, until it sinks into the lunar night. Even at
the very terminator, where the flattest hillock, with
no measureable slope, is at least indicated by half-
tones, the floor of the moon that bears these rays does
not show any elevation. This does not mean, of course,
that the heights may not in places be as bright as the
rays ; but the material of these streaks passes over all
sorts of country, hill, valley, and plain, and without
any deviation, and clearly does not of itself imply any
elevation of the ground. It is just as if one made
pencil marks on a pale-cream globe with features in
relief, leaving the marks of the pencil against the
white ground over all the ridges and those parts of the
plains between them that are lightly touched by the
pencil. Hence the lines are series of shapeless spots
and groups of spots ; there is not a continuous pencil

90 THE MOON

mark'. This is the real structure of the streaks. They
do not exactly ' radiate ' from one point, even where
they are found in their most perfect form ; and they
may be most irregularly crossed, bent, serpentine,
interrupted, or varying in width.

Let us take two striking specimens of the different
species of rays. One of these lies about Tycho, near
the southern border of the moon ; the other about
Copernicus, in the north-eastern quadrant. Their
rays are as different as possible in structure, detail,
and extent. Tycho throws out its rays all round like
the centre of an explosion, so to speak. Copernicus
is surrounded by a veritable network of lines — straight,
curved, and serpentine. In each case the point of
unity, as it were, lies in the common centre.

As regards the Tycho type of rays, which we find
in just the same form about the small-ring mountain
Kepler, one of its most distinctive features is that the
separate rays reach out far from the centre, and,
quite differently from our experience of the explosive
scattering of matter, run to fine points at the end.
Others have the lines of the same width throughout.
Their contact at the point of departure, the base of
the streaks, must not be understood in the sense that
the geometrical centre of the ring-mountain in question
(Tycho, Kepler, Aristarchus, Proclus, Anaxagoras, the
small crater A to the north-east of Furnerius, the still
smaller one to the east of Stevinus, a crater to the
east of Cavalerius at the extreme eastern limb of the
moon, etc.) is the exact starting-point of all the rays.
In the case of Tycho itself, the largest and most
extensive centre of rays, the three finest lines (to the
north-east, south, and south-east) run rather at a
tangent to its eastern and south-eastern walls, and
many sheafs of rays that run toward the west take their
rise in the direction of the southern wall. In number
there must be about fifty lines, without counting fine

Fig. 28

Systems of rays and streaks round Tycho and Copernicus. (Tycho is at the
top of the illustration, Copernicus a little below the middle to the right ; the
dark ' eye ' some distance below it is Plato).

D2 THE MOON

brush-like ramifications which even the practised eye
would find it no easy task to separate in the strong
light of the moon. In the Copernicus type also some
of the lines start from inside the ring-mountain, and
some from its encircling wall. As to the length of the
Tycho rays, for instance, which determines the area
of the system over which Tycho dominates, in a sense,
we may say that an error in calculation has led to an
enormous exaggeration in this respect. Until a very
recent date the streaks that belong to the crater Bessel
in the Mare serenitatis have been put to the account
of Tycho. In this way the longer streaks were made
to cover fully half the face of the moon, if not more.
It is impossible to assign a limit to them, as they have
a considerable strength at the very edge of the disk,
and cannot be traced beyond. This part of the
corona, therefore, with its 3,000 miles long rays,
would reach twice as far as the longest of the other
streaks, which is difficult to conceive. In fact, the
Bessel-streak forms a distinct angle with the radiants
from Tycho, and, if it has any connection at all with
other rays, points rather to the north, where it is met
by one from the other side.

There are many conjectures as to the nature of
these mysterious appendages of the ring-mountains
(and many others). They remain one of the greatest
riddles of the moon ; and this is largely owing to the
reason we stated previously — the obstinate retention
of the Laplacean theory of the formation of the
heavenly bodies and the volcanic theory. Madler paid
little attention to the opinion of Herschel and others
that the streaks may possibly be streams of lava ;
and he dismissed the theory of a real and literal
radiation with the brief remark that the rays are clearly
seen while the centre of the supposed radiation still
lies far within the unillumined part of the moon. ' It
only remains, 5 he said, ' to suppose that, through some

THE MOON 9&

natural process or other, the internal structure of the
floor of the moon at the points where these lines are
seen has experienced some change that has greatly
enhanced its power of reflecting light. What kind of
a process this was is at the most a matter of conjecture,
but there can be no doubt that it was most closely
connected with the formation of the ring-mountains,
which are clearly the central point of these streaks,
especially as these ring-mountains are the only con-
spicuous objects in their regions on the full moon. 5
With all respect for the authority of the great master
of selenography, his successors have pointed out the
untenability of the view that glowing gases issuing
from beneath the lunar floor may have brought about
a partial glazing of the strata. Why did not the gasea
escape from the numerous vents that already existed ?
What made those vents, if gases with an obvious
explosive character could not do so ? And why wa&
the matter only melted in patches (especially on the
elevated parts) and not along the whole length ?

If we turn to the meteoric hypothesis, which would
explain the colour and length as a sort of splash of
the matter of the falling body, which has been resolved
into its elements and spurts outwards with explosive
speed, we have a serious difficulty in the length of
the rays. Experts speak of rays 3,000 miles long.
There is also a difficulty in the form, as the rays are
not of an indefinite breadth, but run out to a fine point,
giving the impression of a force that gradually spends
itself. Hence Nasmyth's attempt to illustrate the
form, at least, of Tycho's rays from the analogy of a
glass globe full of liquid that bursts with radial cracks
when it is heated is so striking that we find his illus-
trations still often reproduced in popular works. But
what a brittleness and cohesion the idea postulates in
the comparatively thick shell of the moon ! And why
should the seams be interrupted so often and make

94 THE MOON

their appearance further on ? The heights usually
show traces of these light lines, and so the ' seams '
must have overcome some great obstacles, and yet they
are often not to be found just where we should expect
them more easily. Finally, even if a meteor was
capable of throwing up a ringed wall of the size of
Tycho, it would never have had the force to break in
so large a part of the shell of our satellite, and Tycho
is less in size and mass than a good many other ring-
mountains. Moreover, Tycho lies on the surface, and
must, as the surviving rays indicate, represent a
relatively recent form of lunar activity. If ' the thick
encrusted moon ' had received the impact of a pro-
jectile at this time it would hardly be likely to be
broken.

Thus the failures of selenologists teach us that it
is impossible to read the hieroglyphics of the moon with
any of the hypotheses as yet offered to us. The
crowns of rays spread out over the face of the full
moon, and seem to mock at all explanation. Possibly
we have only to abandon the earlier ground and the
current theory of the formation of the heavenly bodies,
and substitute for their acute forces and processes
such as will allow more time for the moulding of the
moon's features ; to regard as the outcome of a steady
activity what we cannot explain by explosions and
collisions. Such explanations are quite feasible, but
it is not our place here to enter upon a study of these
possibilities. As every theory of the formation of
cosmic bodies must be tested on the moon, the future
will decide which of them affords the simplest ex-
planation.

Before we go on to describe the mountain-forma-
tions in detail, we must say a word about the general
outlines of the moon. Within the disk the elevations
offer us very much the spectacle that meets the eye of
an aeronaut when he looks down on a hilly country from

THE MOON 95

a great height in the morning or evening. He looks
down on top of the hills, but the oblique illumination
of the scene by a sun that is low on the horizon brings
out the various inequalities of it. It is otherwise at
noon, when all shadows and profile disappear. It is
much the same in observing the moon ; though the
mountains, either peaks or ridges, that lie very near
the limb, can be seen at any time in their true shape,
height, and slope, as we are in the position of an
aeronaut passing over them when we examine them
in the telescope. At certain parts of the disk, which
vary slightly in virtue of the process of ' libration '
that we have already described, we perceive the very
marked profile of mountains, and this gives a lumpy
appearance to our satellite. This unevenness of the
limb unfortunately interferes with our measurement of
the moon's diameter. It must differ in extent accord-
ing as there are mountains or plains at the limb at the
moment of measuring. Strictly speaking, therefore,
all measurements of the moon must vary within certain
limits. The average diameter is something between
2172 and 2150 miles. There are, it is true, other
causes of variation. There is, for instance, a fairly
wide region about the equator where the moon is
strikingly flattened, on account of the presence there
of what Professor Franz has called ' Mare Smythii '
(237 miles broad). There is also a ' Mare marginis '
{Professor Franz) within the selenographic range of
the Mare crisium near the limb, of only slightly smaller
dimensions, so that the scanty upland between the
edges of the two stands out at an obtuse angle. These
divergences from the globular form often cause mistakes
in a certain class of lunar measurements and eclipse-
observations, and these must be corrected by paying
attention to the libration at the time, and its influence
on the curvature of the moon's surface. Of recent
recent years Hayn has determined and published the

96 THE MOON

corrections for the departure of the limb from the
standard.

Near the moon's limb we see the profiles of the
mountains at a glance. Towards the middle of the
disk we can at most only find them when the summits are
illumined by the rising sun, and then the slopes slowly
emerge out of the night ; or when, on the other hand,
the successive parts disappear at the setting of the sun.
We often see whole chains of peaks, the outlying points
of an irregular ring-wall, flash out on the torn terminator
like so many pearls, gradually growing more and more
numerous, until the loose string gets thicker and
thicker, and reveals itself at last in the form of a solid
ring. The magnificent spectacle of the lunar sunset in
the ring-mountains is further enhanced by the sharp
contrast between the deeper parts still lying in the
black night and the brilliant row of the pearl-like
peaks. With mysterious and measured pace the
illumination passes down the slopes, and embraces
gradually the seemingly unfathomable mouth, black
as a pit. Suddenly a point in the centre creeps into
the light. The phenomenon began with a soft light
as of the dawn ; the eye can follow its increase step by
step ; and in a few minutes the rays proclaim that
the sun has reached the central peak. It grows clearer
and clearer, and rises with ever-broadening base from
the encircling night, like an island emerging from the
sea at the ebb of the tide. A few hours later the light
penetrates into the seemingly fathomless depths, and
then the ring is revealed in all its glory to the gaze of
the observer, who can follow the structure of the
curious lunar mountain with perfect ease. The ridges
that were first lit by the sun bleach slowly in the light,
the later illumined parts follow with a yellowish tone,
and with them is mingled the deep black of the shadows.
As the hours go on the shadows become smaller, and
what they had revealed in sharp angular outline, as if

THE MOON 97

a practised hand delineated them in thick strokes,
grows softer in the lingering half-tones, as in a crayon
drawing. The relief is so far lost in the waxing sun-
light that we can at length only trace a faint plan of
it in white lines.

For a few days we have this vague harmony
instead of the initial contrast of height and depth.
Then the play of light begins afresh in the reverse
order. Within the lengthening shadows, stage after
stage of the hill sinks into the darkness. The last
peaks disappear, and the fourteen-day night sets in,
relieved only by the earth-shine which our ' full earth '
now casts on the new moon, just as the gentle brilliance
of the full moon illumines the earth at night. But 1
the earth is much larger ; it has a diameter 3£ times
the size of the moon's. Hence it stands out in the
nocturnal sky of the moon like a great disk thirteen'
times as large as the moon seems to us. It illumined
the moon almost in the same greater proportion to
the moonshine reflected on earth, and so allows
terrestrial telescopes to recognise even small featured
in the earth light r and teach us for certain that the
distribution of bright and dull spots on the moon is
essentially the same during the long lunar night a& in
the lunar day. Yet the belief that there is a slight
alteration of tones is not wholly groundless. It will
be one of the pleasant tasks of the future to study the
phenomena of the ' ashy-gray light,' at least three or
four days before and after new moon* and this will be
done best in southern climates.

CHAPTER IV

The Ring - Mountains

At a time when it was impossible to calculate
exactly the size and steepness of the round lunar
structures, they were all, from the largest to the
smallest — and the very small ones were not known then
—comprised under the general heading of 'craters.'
The name has now become a merely formal expression,
but we inust show on what ground it came into use
at all, so that it may be properly understood. Their
appearance, as will be seen even on small pictures of
the moon, shows how the name would be quite satis-
factory for naive observers, and its convenience as
an expression of at least one aspect of the objects
justifies the continued use of it. But it is more
interesting to study the radical differences in structure
between terrestrial and lunar ' craters,' quite apart
from the enormous size of the latter.

A mountain that has been formed from the
plutonic matter of the lower levels of the earth, under
volcanic conditions, will have the distinct form of a
cone, because its mass, which is generally very con-
siderable, has been gradually ejected, during long
spaces of time through a comparatively small opening
in the earth's crust. The dome-shaped curve of a
mole-heap is hardly ever seen on the moon ; though
there are objects something similar to them, which we
have already called small bosses ( ( boils') with

THE MOON 99

craters on them. There is a number of them on out
map of the Cauchy region. The typical form of th^
objects that the geologist calls an elevated or eruptivi
crater is a cone. At its summit we find a trace of thi
opening from below, though this is sometimes partly
closed, sometimes pierced by another crater of smaller
dimensions, which still preserves its opening, and ik
active volcanoes ejects sulphurous gases and ashes).
Lava-streams usually break through the side of &
volcano. I

An eruptive cone of this type would hardly bja
visible in the largest telescopes, if it were transferred
to the moon. A lunar crater is a fundamentally
different type of structure. In the first place the piafr
of its construction is quite the reverse to that of ja
volcano. Its ' crater ' does not lie on the summit ^f
a cone (see the profile map) ; it is merely a wafy,
generally composed of a ring of elevations, withijn
which there is a more or less level surface, often strewfr
with mountains, hills, bosses, cavities, small craterp,
ridges, and bridges, and so deeply excavated that it li^s
far below the general level of the moon. Lun4r
craters, therefore, are cavities or depressions, n<H
elevations. In order to reach a terrestrial crater oije
has to ascend mountains thousands of yards * high, arid
then to descend only a moderate depth ; to get into
the depths of a lunar crater one would have first to
ascend a broad upland of moderate height (the waflj),
and one would then look down from a ridge onia
succession of terraces, leading down with fair steepness,
steeper as a rule than the descent from the higher
plains of Mexico to the coast. To form a just idea <)f
it we may picture the scene in this way. Put a flit
dish floating in water. The water will represent tlie
generaHevel of the plain without ; the deeper interior
of the dish gives an idea of the interior of the lunar
crater. If we then put the same dish — assuming it

Fig. 29
The Half Moon

THE MOON' /-, \ \ '-I'^'/C-i'^i ?P1

to have a raised curve round the bottom— upside down
on the table, it will illustrate the depression that we
sometimes find in a high district ; say, the Wan Sea,
or the Goktscha Sea (Ararat region). In the terrestrial
case we have a slight depression at a great elevation ;
on the moon. a moderate elevation and then a deep
cavity, (compare the profile picture).

We may plausibly generalise from these characters
and say there is so great a contrast between terrestrial
and lunar craters that it becomes easy to doubt whether
volcanic energy is responsible for the latter. We are
well acquainted with Neison's view that there are some
' real craters ' on the moon. ' It is difficult to discover
these crater-cones on account of the smallness of
their mouths, and they are easily confounded with
the bright peaks of mountains.' Klein, also, who
spent thirty years in observing the moon, says some-
where of the half -sunken round formation Stadius,
near Copernicus, that the small craterlets on its level
stand on a high substructure, so that they look like
needles when the sun is low. Both these ideas of a
certain sort of small ring-structures must be modified.
There are no objects at all that will bear a direct
comparison with terrestrial cones. The plains in
Stadius and to the south of it have only a slightly
rougher relief than many others* as we can easily see
in a strong light.

In point of size the walled plains occupy the first
position on this hemisphere of the moon. They are
depressions of a marked or a moderate character, such
as Clavius or Grimaldi, clearly showing the" curvature
of the lunkr globe, especially when they are very close
to the limb, and when their floor is flat. The finest
specimen is Clavius, with a diameter of 145 miles.
Its depth is jVist as striking to the eye as it is proved
by measurements, and it has a whole range of forma-
tions of the sec6nd and third rank within it. Its high

•••-••

• ••» • •••••••

102 2 :.. : >: .. ; •: : : .•;„ .tjie moon

border is pierced by large crater-rings. It is larger
than Wales, and is remarkable for the purity of form
of its ' crater-cone.' It is iri this and its subsidiary
forms that we best see the weakness of the volcanic
theory.

At the south-east edge of the moon we find the
partly obscured plain of its rival Schickard, a long-
drawn ellipse 125 miles in length. Its floor looks like
the convex bulge of a shield, and clearly shows the
curvature of the moon's surface. Its surface, moreover,
is not much broken by subsidiary features, but
comparatively flat, though perhaps a little lower to
the north and south than in the centre. Schickard
has also an outwardly more independent wall with
numbers of ridges and passes, which is a general
character of these larger structures. Hardly less in
size, but with a very different border — massive hills
at one point and flat shore-banks at another—is
Grimaldi on the eastern limb, with a diameter of 120
miles, and very little appreciable detail on its curved
and very darkly-coloured floor. Owing to its position
amongst bright uplands and its own darker shade it
might almost be included amongst the ' seas.'

Humboldt in the south-west and Bailly equally
close to the limb on the south-south-east measure 112
miles across. The former resembles the two already
described; the other is like a field of ruins, strewn
with ridges, hills, and craters, all enclosed in a common
border. In the centre of the moon's disk there is only
one giant-structure, the typical Ptolemaeus, with a
diameter of 100 miles, and strewn with details of all
sorts. As this is well exposed to view in all phases
the author has discovered and charted no fewer than
78 craters of the second rank, 8 depressions without
walls, and 10 seams within the huge circle, as well as
90 hilly ridges and 16 craters on the wall.

THE MOON 103

Another that is almost as large and rough in detail
as Bailly is J. Herschel in the north-east. A little
smaller (93 miles) is, Gauss, an almost empty plain,
with merely one fine and prominent central elevation,
to give a clear impression of a ring-mountain of the
crater-type. About the same size we have Petavius
in the south-west (in the vicinity of Humboldt) with
a very distinct wall, divided into parallel sections, and
a fine central mountain 19 miles in diameter. Hippar-
chus, also about 93 miles in diameter, in the nighbour-
hood of Ptolemaeus, has a good depth and a pentagonal
outline. Its steep inner wall is pierced by gigantic
passes and set with subsidiary crater-forms ; its floor
is strewn with veins, hills, and a 19-miles wide ring-
mountain.

These huge objects complete the list, if by walled
plains we wish to understand only the larger of the
round structures. Neison does not take the word in
this exclusive sense, but includes structures down to
40 miles in diameter. Besides a few objects which
we have not yet mentioned, this definition will bring
in structures of the type of Archimedes (51 miles) and
Plato (60 miles) on the one hand, and of the type of
Tycho (52 miles), Copernicus (57), and Arzachel (64),
on the other. The former may very well be described
as walled plains, as the name is as literal a description
of them as one could wish ; but the latter are well-
formed ' craters ' with a central elevation. In these
it is not the plain that chiefly catches the eye, but the
terraced slopes and the central mountain. It is best
to take into account the general impression of an
object in giving it a name, and so we must classify
even much smaller structures as walled plains (such
as Kies, Lubinietzky, Billy, and Herodotus), as these
cannot very well be given a different name except
under the influence of some theory or other.

104 THE MOON

We must not be understood to take exception to
the lunar nomenclature in these remarks, as it can be
worked up into a formal system without doing any
harm. We wish to show merely that the various types
are to be found in all sizes and all stages of their
characteristic features. Neison restricts himself so
little to the ground he chooses for division that he puts
the c ring-mountains ' immediately after the walled
plains. From the following description of the charac^-
ters of the best-known forms we can understand how
the group is arranged. First there is Copernicus, its
floor, 57 miles in width, scantily encircled with walls
of a partly unduiatory and partly broken-up character.
To the west of Copernicus lies Stadius, 31 miles wide,
its horse-shoe shape clearly being the remainder of a
once complete circle, and its low walls pierced with
many holes. To the east and west of the small crater
Wichmann there are other ruins of the same kind ; and
not far from them there is a crown of isolated peaks
near Flamsteed, which strikingly mark out a circular
space 65 miles in diameter, and must be regarded as
the outstanding heights of a sunken structure. Finally,
there are many levels with low ridges belonging to the
group which only catch the eye when the sun is low,
as we find to the west of Copernicus and round the ' long
wall ' of Thebit, where the region so defined measures
1.12 miles in diameter. The more specimens of this
sort we consider, the clearer it is that any description
that suits the chief characters of a lunar form will
suffice, as long as it does not involve any theoretical
conception or any idea as to their origin.

However, Neison goes further, and describes in
succession ' ring-plains,' from 56 to 20 miles in diameter,
in which the area of depression is very large in pro-
portion to that of the wall ; ' crater-plains/ 20 to 12
miles in diameter, which appeal to the eye as craters
in spite of their vast size ; ' craters/ in which the

THE MOON 105

inner surface is much smaller in comparison with the
well-formed mass of the enclosure (4-12 miles) ; and
finally, 'small craters, 5 of still less roughness and of
such dimensions that they are only seen on close
observation.

A walled surface large enough, for instance, to
enclose the whole of Manchester, seemed to the earlier
observers to betray a ' volcanic origin.' Neison does
not hesitate to describe depressions of 4-12 miles in
width as 'the real lunar craters.' It is always the
volcanic theory in the rear that influences research
and description in this way.

Besides the four classes we have enumerated he
gives also 'crater-pits,' from a few hundred yards to
6 or even 11 miles in width, with very scanty or
totally unrecognisable walls and ' crater-cones ' —
'perhaps the only real representatives on the moon
of our terrestrial volcanoes' — with a comparatively
small opening in their lofty and steep summits. We
have already pointed out that there are no such
objects anywhere on the moon. The first glance at
elevated craters of sugar-cone form may be deceptive,
but the experienced observer must have restraint
enough to take into account the low and one-sided
position of the sun, when he sees the remarkably long
and pointed shadows. It will always be found that
both the curve and the absolute height of these
* elevations 'or ' eruptive craters' are very considerable.
Certain structures of this class in Stadius cast shadows
20 miles long with the sun at 2°, yet they have a base
averaging two miles broad to a height of only about
550 yards, and so do not justify the comparison.
Moreover, these structures are very rare. We must
bear in mind, too, that the smallest and the largest
ring-formations are all composed of the same material.
If this is of such a nature that it does not present
knife-like ridges, but seems to round off the edges and

106 THE MQON

angles, the depression on a - small elevation must
naturally seem narrower and flatter than if it had a
broad base for its development. As the author has
not felt compelled to admit volcanic forces, he has
never found any necessity for introducing a finely
graduated nomenclature. Any student who bears in
mind the details of the size of lunar structures in
describing them will be sure to avoid misunderstanding.
We cannot refrain from mentioning at this stage
a peculiar form of ring-structure that is found in a few,
but well-formed specimens — the sunken walled plains
on the edge of the sea. They have sunk more or less
sympathetically in connection with the subsidence of
the sea-floor, and they reveal the destructive influence
of their neighbour, either in obvious undermining of
their wall, which has become invisible at some points
and entirely sunk in at others, or in the disappearance
of a large part of the area, at least as far as certain
peaks. To show how we find the phenomenon in all
its stages we will describe a few more lunar forms. On
the north-west border of the Mare serenitatis there is
the walled plain Posidonius, some 62 miles in width.
To the east the wall has become very thin and low,
and a mile and a half of it has disappeared altogether,
so that the level of the Mare and the interior surface
is almost the same. This is the case of slight defor-
mation. On the diametrically opposite side of the
disk is Gassendi, at the edge of the Mare humorum,
56 miles wide, with the whole of its southern wall
submerged with the Mare ; the. latter, in fact, seems
to have penetrated it by a wide breach, as a broad
patch on the inner wall is dark coloured. But the
rest of the wall is intact, as we also find in the object
Pitatus on the south shore of the Mare nubium ; about
one-fifth of its area slopes strongly towards the sea,
and there, is a wide breach that shows the equality of
level .on either side. A fine example of this type is

THE MOON 107

found in Fracastorius on the south shore of the Mare
nectaris. This huge ruin has lost a full quarter of its
enclosure, only a few groups of peaks and dams remain-
ing to show its former position. Its interior bristles
with hills, craters, bosses, dykes, and breaches, and
the part of the wall that remains at its full height is
pierced by a good many secondary craters. Almost
exactly like this immense horse-shoe of 56 miles
diameter is the half -crater on the southern edge of the
Oceanus procellarum of still larger dimensions, Letronne,
which has lost quite a third of its northern wall, not
even a single peak now rising out of the Oceanus.
The # inundation has not entirely destroyed the two
central elevations, but there is hardly any other detail
inside it beyond a few flat ridges. Another structure
that has lost fully one half its wall by subsidence and
inundation is Lemonnier on the western shore of the
Hare serenitatis, of which only a few ruins are left on
the eastern side. There are also smaller objects of
the same class, such as Hippalus, which has lost a
third of its ring- wall, and is full of ruins. Not far
from this, on the eastern side of the sea, there is
Doppelmayer, which has merely suffered a considerable
subsidence, like Gassendi in the north. We could
enumerate a good many of these smaller objects, as
well as others that have more or less subsided inside
the walls. Of this nature are one to the east of Encke,
two mountain-circles to the west of Letronne, Stadius
to the west of Copernicus, a horse-shoe structure to
the north-west of Aristarchus, a flattish form named
Kies, Beaumont, near Fracastorius, some scanty
remains of a ring-mountain on the northern area of
the Mare nectaris, the mountain-circle round Torricelli,
two sunken forms in the Mare crisium, etc. ; to say
nothing of the numerous bays which either run into
the highlands or seem to be relics of former crater-
cavities. In these we see the same effects as are

108

THE MOON

found at the edges of extensive submerged areas on
the earth, but without the accompanying phenomenon
of the violent storms that bring the land to a common
level. That is a specifically lunar feature.

There are three other sorts of lunar forms that are
very interesting and are fatal to the current volcanic
theory. The first category contains the double and
multiple objects with a common interior. We have
a fine specimen of this class in Torricelli, whose 12 mile
broad ring has an appendage 6 miles in width, giving
rise to a pear-shaped structure. To the north-west of
this, on the edge of the heights, there is a still larger
specimen ; and to the east of Torricelli there is a
flattish, elongated depression called Hypatia. To the

Fig. 30. Aiiyd.

Multiple craters

Fig. 3 1 . Copernicus A.

south of Copernicus there is a double structure (see
illustration), with common interior ; on the outer edge
of the walled plain, Albategnius, there is a triple one,
known as Airy d, which looks as if it had a double

THE MOON 109

constriction. There is a very similar triple structure,
though the division is less advanced, called Reichen?
bache, with a length of 42 miles and an almost smooth
floor. But these objects are insignificant beside the
large double structure in the extreme south-east that
has the name of Schiller. It measures 112 miles and
consists of a smaller half, which is filled with hilly
ridges, and a larger half with a smooth floor. It is
very difficult for the volcanic or the meteoric hypothesis
to explain structures of this kind in any intelligible
way.

The other sort of lunar mountains also is unique,
and is not like anything on the earth. These are the
connected ringed-walls, which may be fairly concentric,
or may merely overlap, but cannot very well be re-
garded as twin craters, like the form Copernicus A,
One of the two is always intact, and looks as if it had
eaten its way into the wall of the other. One of the
most characteristic examples of the class is the pair
Theophilus— Cyrillus (sec Fig. 9). The first crater-
plain is quite round ; but if we were to complete the
northern wall of the other, its crest would extend some
12 miles further, and the rings would overlap to the
extent — they are about equal in size— rof qne-fourth of
their area. At first glance we should say that the
complete object must be the more recent, the imperfect
one the older. That is certainly bound to jbe thp
opinion of the volcanist, but it is quite wrong. In
details the volcanic theory has always proceeded pn
speculation rather than on research, and here at least
it breaks down. When we take into account thp
phenomena of fragmentary craters, sunken ring-
mountains, multiple structures, and the extraordinary
flatness in proportion to the diameter, it is more reason-
able to suppose that, in a way we will not attempt to
explain just yet, the imperfect object has grown on to
the other, much as outlying walls in a fortress are

110 THE MOON

built on to the main wall. This growth cannot have
been one-sided in the present case, or in Thebit, or
Zagut and Guttenberg and Hainzel, but must have
been mutual, the two ring-walls embracing each other
as it were. In other cases the walls are concentric, but
these are more easily explained by the operation of
central agencies. • ' '

The third kind of lunar peculiarities are the almost
square Area in Aristoteles, the similar square of vast
proportions, W. C. Bond, 1 an enclosed square space in
Eratosthenes, another in Theophilus (north-east), and
several others. These can hardly be volcanic in origin;
even if other forms were. At every step we meet struc-
tures that militate against the theory.

We have spent some time in these observations,
although one must admit that the small maps that the
general reader can consult in an atlas or encyclopaedia
are very imperfect guides through the labyrinth of
lunar forms, and the names of all the objects we have
described will not be found in them. But there are
so many writers at work to-day popularising scientific
knowledge on the old base of the Laplace theory that
it is absolutely necessary to draw attention to a source
of facts on the moon that does not tally with it. This
source is the rigid face of the moon, unchanged for
countless ages, whose stony features contain the secret
of its origin. It is our work to find the solution of the
enigma, just as, some decades ago, we found the key
to the cuneiforn writings.

At a time when lunar science was in its infancy and
observers had quite enough to do in the work of collect-
ing facts, it was possible for speculation to make bold
ventures, without the risk of their being contradicted
by actual observations. But for the last twenty years
or less, selenography can boast that it has discovered
abundant evidence to refute the old idea that the moon
is an off-shoot from the earth. * Every attempt to read

THE MOON 111

lufiar hieroglyphics on the theory that it is of a volcanic
nature and was composed of material directly similar to
that of the earth could not get beyond the most super-
ficial characteristics. It only remains, therefore, to
pour our new wine into new bottles, to remember that
our companion has only a specific gravity of 3 '5 and
gives no indication whatever of volcanic character, and
base our speculations on its peculiar and distinctive
features rather than on the ambiguous and too general
characteristic of the circular form bf the mountains. We
can only say as yet that there is some prospect of success
in that direction.

The number of the ring-structures arose from
a few dozen on the older maps to several hundred on
Tobias Mayer's map. Schroeter added many objects*
but it was chiefly Madler and Lohrmann that increased
the number. Madler' s * Mappa selenographica ' indi-
cates 7,735 crater formations, and Lohrmann's valuable
and independent, though almost contemporary work
gives 7,178. The difference is that, though Lohrmann
had a larger instrument, Madler used a somewhat finer
one in Beer's observatory, and perhaps had better con-
ditions in the Berlin Tiergarten. It must be riemem-
bered, too, that Madler' s fine ' pits ' are often misinter-
preted, whereas Lohrmann's work is very faithful and
objective. Schmidt indicated no less than 32,856 of
these ring-structures — disregarding the others for a
moment — on his six-foot ' map of the mountains of the
moon.' The revisers of the map were in a position to
add more, and the present writer has himself contributed
4,590 * craters ' in regions on which he happened to be
working. Schmidt thtfew out the conjecture more than
a quarter of a century ago that there would prove to be
100,000 of them when it became possible to apply a
power of 600 to the moon. He t^as quite right, and the
author has found that half that power is sufficient. The
best instrument is an experienced eye. The wealth of

112 THE MOOST

form that is immortalised on Schmidt's map can only
be appreciated by those who make use of it, but if the
above estimate is right we should find ten craters to
every part of the map that could be covered with a
farthing. The number of other lunar features is legion.
It could not be expressed in figures, and could not
possibly be crowded into Schmidt's map,

Let us now transport ourselves in imagination to
the three-mile high peak on the western wall of Clavius.
We are looking eastwards over the depression of the
plain, at a time when the sun has passed over the spot
some days before. Our elevated position enables us to
trace an almost closed ring round the depression. But
the eye cannot reach the further side, because even
at a height of three miles on the eastern wall we cannot
look over the hills that fill the interior of the plain and
limit the horizon. Before us is, at a distance of 43 miles,
a large crater 17 miles in diameter that at once catches
the eye. Its rough outer slopes have numbers of wrinkles
and off-shoots, that merge gently into the plain. Its
crest has no lofty peak, like those that line the crest
of Clavius itself to our right and left. In front of the
circle we see flat banks and rough bars scattered across
the scene, They are the flat ends of the rugged spurs
from the north of a second giant crater, which lays its
mass against the inner wall of the ring. It is nearer tp
us, and we can see its deeply furrowed north-west side,
which is turned towards us, glittering in the sun, or
darkening in its deep clefts, or still, in places, casting
its black, hard, and angular shadows. The space ber
tween this mass of rough contours and the western wall
of Clavius itself, which spreads out at our feet, is milder
and milder as it nears us. On our left it is like the
colossal ruin of mountain spurs that have run into each
other, and immediately below us they have arranged
themselves in a parallel series of descending terraces.
Our eye cannot reach the foot of our wall, which is some

THE MOO* 113

nineteen miles away, because in front of us the inner
side of it rounds its great slope like a deep-breathing
breast. After a few rough stages a wide cavity opens
its gaping mouth behind the sharp crest of the last
barrier, and we seem to look down into an abyss. Its
depth may be judged from the impression on the ob-
server of the plain that rises beyond it, like the surface
of the sea seen from the coast. On our right also we
recognise a giant-crater, with the crest of Clavius hanging
vertically over its ring, and showing that there has been
a wide breach in the main wall of the crater. The great
structures that we see rising to the south and the north-
east cover the larger part of the main crest. In the
east-south-east there is a narrow opening through which
we look out on masses scattered like ruins over a distance
of 47 miles, and catch the jagged line of the south-east
wall 106 miles away. To the east-north-east also we
see the outline of the great wall as a gleaming white on
the black background of the heavens. Right behind
the first-named crater, which bars the prospect toward
the east, we catch a glimpse of another large one at a
distance of 70 miles, also covered with small undulations.
If we look behind us we see no great gulf yawning, but
the eye is dazed by the flood of sunlight that pours on us
and the brilliant white of the strongly-reflected slopes
near us. The eye is hurt by the contrast between the
brightness all around us and the deep black shadows of
the depths below and the equally dark sky above. The
brain is bewildered if we attempt to cover the chaos of
inequalities that stretches out before us in terraces, in-
terlacing rings, craters, precipices, and myriads of
other forms. We should need a much more lofty posi-
tion to get a clear view of all the structures that crowd
together. And we terrestrial observers have indeed the
advantage of taking up a supremely elevated position
and getting a perfect bird's-eye view of the scene — we
look on it from the earth through the telescope. But if

114

THE MOON

Fig. 32 Fiu. 33

Shadow-figures in the walled plain Plato

Fig. 32 by Fauth (morning illumination) ; Fig. 33 by Weinek (evening
illumination).

we have the advantage of height we pay dearly for it in
the matter of distance. We have already explained
that even with the highest powers the moon remains at
a considerable distance.

If we mount the highest western peak of Plato (60
miles in diameter), and contemplate the situation of
this gigantic theatre, more than a mile deep, we find a
quite different spectacle from the preceding one. The
wall at our feet, both in front and behind, is very im-
pressive. Here it seems to descend almost without
gradation into the bottomless deep that spreads out
like the surface of an ocean toward the east : there it
breaks into a wild and craggy landscape. But both the
course of the wall and the plain it encircles are quite
different from Clavius. The crest vividly recalls the
jagged line of an Alpine range in the far horizon (see
illustration).* On the western side we have a series of

*One must remember, of course, that the real aspect of the line of peaks
and crest, as seen in a horizontal direction, would present far less difference in
altitude than the long shadows cast in a strong light would lead one to think.
At the same time these * magnified ' profiles enable us to make much more
accurate measurement of the heights.

The moon

115

Alpine peaks, the three highest reaching 1,722, 2,166,
2,445 yards. Between them are at least seven others of
less altitude that are distinctly Alpihe-in their contours.
One of the passes between the steep-rising peaks is at a
height of 555 yards above the inner surface, another at
a height of 1,000 yards. The conspicuous notches in the
shadow line show that in the western quarter of Plato's
enclosure there is a high peak about every four miles.
If we look toward the east we see before us a real
plain with no important details. It spreads out almost
to the horizon, and is encircled by an undulating wall of
which we cannot see the foot in the extreme distance.
One huge peak in it rises to a height of 2,445 yards : a
straight peak, flanked by two hills in the south, and one
in the north, of less proportions. Twenty-eight miles in
front of us is a flattish boss, which the telescope would

\$fr%t^^:F%

sf^SHs^i^'* ^"~- ■■-■ ililt

i^s

ft's^fe- j^iahjji^jfjy

Ski

Fig. 34.— Map of the walled plain Plato, by Ph. Fauth (1 mm. = 3,031) in.).

4? > : ' <:*■■ • ■ %:/ : TO ""-■ # of r #

Fig. 35— Map of the ring-mountain Copernicus, by Ph. Fauth
(1 mm. = 1,540 m.).

THE MOON 117

show to be a small crater-form about two miles in
diameter. Another one comes into view on the right, and
if we look closely, we can discern with the telescope half
a dozen very flat breaks in the great desert plain of Plato.
The only relief is afforded by a few vague grey spots and
the broken slopes of the wall. There are few of even the
most modest * crater '-structures scattered over the al-
most smooth floor here — -but we will return later to the
subject of Plato's inner surface — whereas there are
dozens in Clavius, and the largest of them measures 17
miles. The comparative level of the plain shows that
the cavity, which was certainly more concave at one time
must have been filled up from below ; though it is not
necessary to bring in the familiar molten material of the
moon's interior to explain this.

We have a different spectacle in a well-formed crater
like Copernicus, which I reproduce here in a greatly
reduced print of my map. Unfortunately the reduction
has much interfered with its clearness ; the original is
on a scale of 1 : 450,000. Here, with a diameter of
56 miles, we have in the western summit A of the chief
crest an excellent position at a height of 3,777 yards,
from which we can survey both the cavity and the
entire wall. In front of us a number of almost isolated
peaks rise out of the middle of the hollow, the one to
the east reaching a height of 750 yards ; the nearer one,
on the west, is about 673 yards high. The whole
group looks like a heap of loosely tumbled ruins, and
is totally unlike what we would expect in a volcanic
cone, though the term * central mountain ' is usually
applied to it. From our eminence A we can not only
fpllow the further limits of the plain beyond these hills,
but can also detect a great difference between the
northern and southern halves. The former is covered
with extremely flat and long undulations, generally
running from south-east to north-west ; the latter has
a large number of peaks and bosses, which seem to be

118

THE MOON

Fig. 36 Fig. 37 Fig. 38

Copernicus according to Tempel, 1860 ; Hefti, 1882 ; and Weinek, 1884
(original size).

Fig. 39

F«G. 40

Copernicus according to P. A. Secchi and E. Neison. (Half original size).

scattered irregularly, though they can really be grouped
together, much as if a number of clods had been
washed into heaps and strings. The generally flat
interior of Copernicus seems to indicate that its level
was formed in a fluid state ; but once more the
•central mountain ' and other characters forbid us to
introduce plutonic forces.

THE MOON MB

All round the eye sweeps over a terraced landscape
on the inner and outer walls, filled with an enormous
number of topographical forms. - It is a chaos of
parallel and transverse valleys, eminences, ridges, and
peaks, alternating with gorges and crater-cavities.
The crest of- the wall itself, which is much deformed
and broken by independent lunar forms, as in the case of
Clavius, departs very considerably from the circular
shape. There are about 11 distinct angles.; some
stretches of the crest are straight, while others are
curved, with the bend inwards. As in the case of
Plato in the east, where a sort of landslip has broken
the line of the enclosure, and caused a good deal of
the wall to fall into the cleft made, so in Copernicus we
find— or at least, seem to find — similar masses broken
away from the main crest in two places. In fact, the
structure of the complicated terrace-system of the
most perfect ' lunar crater ' that the telescope reveals
is one of the greatest difficulties for any explanation
of the action of constructive agencies. It is impossible
to solve the riddle of its mountainous structure on
the lines of the plutonic theory ; perhaps just because
the features — as strange as is their origin— have 1
remained in their original condition.

There are many other features of the moon's face
that we might dwell upon. From the peak of Coper-
nicus, for instance, we need only sweep the landscape
to the west with the telescope, or look out over the neigh-
bouring shore of the Mare nectaris from the western wall
of Theophilus* and we find shoals of tiny craters giving
the place the appearance of pumice-stone or sponge.
Other regions, as in the mountain Argaeus, would look
like a broken coat of ice. But the forms are innumerable,
and we must be content with the pictures we have given.
There is one other peculiar class of structures that
we must mention, because for some time they gave the
chief countenance to the theory that changes are still

120

THE MOON

MZM

Fig. 41. Copernicus, from Prof. Prinz's enlargement. (Half -size.)

taking place, and they are, as a matter of fact, the
most recent constructions of the lunar forces. These
are dark, almost black, spots. It was thought that
they represented the outflow of masses of dark lava,
accumulating in hollows. But there are few cases in
which cavities have been recognised, and there are
others where we have reason to think the ground is
elevated. There are spots of this kind, almost circular
in shape, in the hilly ground to the south-west and to
the north-east of Copernicus, in the plain near Gam-
bart C, on the eastern shore of the Mare nectaris, in

THE MOON

121

Fig. 42
The Alphonsus-spot (Klein.)

Fig. 43
Alphonsus (photograph )

Atlas, Alphonsus (see illustration), Petayius, Schickard,
Biccioli, etc. Criiger, Billy, Endymion, Vendelinus,
and Grimaldi have a smooth dark sea-surface generally,
and are only one step removed from the Mare crisium.
From these we can draw certain conclusions with
regard to the processes that produced the ring-forma-
tions with smooth floors, or have left in other walled
p!ains certain marks of recent action in the shape of
blackish spots. We often see small craters in the
middle of, or at least inside, the spot — they can also
be seen at the borders — and these are regarded as the
natural outlets of the dark matter. But, once more,
there is no need to assume any ' dark-coloured lava '
or a thin layer of ' dark ashes ' ; if that is done, we
may well ask how it is that the five walls of the little
craters and hills have remained white. But we know
from what we have already seen that no physical
problems of the moon can be solved on these antiquated
plutonic lines. We shall afterwards describe a way in
which the question can be answered much more simply,
and from which side-paths branch off toward the
solution of many cognate problems.

122

CHAPTER V

The remaining Elevations and the Rills

The solid mountains on the moon form a special
class, although they seem, on a superficial examination,
to resemble closely those terrestrial mountains which
have an extensive surface. But we should conduct our
task of exploring a foreign world very poorly if we
were content with a superficial analogy, and did not
make a more searching examination of our phenomena.
Doubt is one of my best leaders into the unknown :
the most effective impulse to fresh work. In the
present instance it is greatly aided by the facts them-
selves, which are by no means easy to ascertain. We
may say, without hesitation, that the typical specimens
of lunar mountains — The Apennines, Alps, Caucasus,
Hsemus, Carpathus, Riphseus, etc. — are as little as
possible like terrestrial mountains in structure. If we
wanted to give a proper and instructive description of
the lunar highlands, we might say : The Apennines
(see Fig. 3) form a conglomerate of elevations and
depressions (or ' intermediate spaces ' ) on a base that
is slightly bent towards the south. We must regard
the base as a piece of the earlier shell of the moon
(we deliberately avoid the word ' crust '), which has
been broken off by some remote agency and has been
lifted up together with a colliding piece to the north,
that was at first submerged and then reared up once

THE MOON 123

more (but pushed a little more toward the west).
Thus, if we regard the base of the Apennines as an
oblquely raised surface and the ring-format : ons of
the Mare imbrium as incomplete elevations, or ele-
vations inundated by lunar matter (and partly filled
up, as in the case of Archimedes), and explained on
the analogy of the rest — ' explained,' that is to say,
on the lines of the theory that substitutes for the
' magma ' (for which there is no place on the moon),
another fluid with similar properties of expansion and
solidification — we shall find increasing evidence in
favour of this new material.

Figs. 44-48— a, a Pico ; b, b ' Piton ; c, Lambert, N.W.

In the first place, besides the perceptible rise on
the Mare-side in the Apennine base, and, to a small
extent, in the base of Carpathus, we find that all the
solid mountains, and this is especially clear in the
Alps, consist altogether of peaks and crests. There
is nothing of this kind on the earth, with the exception
of the Greek islands, which rise out of the level of the
Aegean sea like so many warts, bosses, hills, and
peaks. We have something similar in the shoals of
islands off the coast of Norway, Sweden, and Finland.
The sea makes an even level from base to base ; the
hills do not slope gently upwards, but rise straight
from the surface. It is just the same in the vast
region occupied by the lunar ' Alps. 9 Here isolated
mountains and groups of hills are scattered over a

124

THE MOON

light-coloured surface, and rise like islands out of the
ground ; it is only at the eastern bluffs of the mass
that we find large masses heaped up, but these are
not connected together like terrestrial mountain-
masses — especially bearing in mind ,z that the Swiss
Alps are not shown on our maps in their original form,
but weathered and worn by the action of water during
thousands of years, while the lunar topography
remains in its virgin freshness. Further, the lunar
Alpine mass is burst at two places ; at its main outcrop
on the east, where the high peaks and steep bluffs are,
and again, transversely, at the point where we now

Figs. 49, 50, and 51. Situation of thej valley of the Alps, according to
Webb (W), Elger (E), and Gaudibert (G). (A slightly enlarged reproduction).

THE MOON

125

see the great ' valley of the Alps.' 6 miles broad and
more than 80 miles in length*. The slight depth of
these broad gaps and their level floor countenance the
idea that the bursting of the mass allowed the fluid
to rise almost to the edge of the breach. The cleft

Fig. 52. The great vallev of the Alps.
January 25th, 1885).

(Drawing by Th. Gwyn Elger r

* The author's own map, which is also given, represents the actual condition
of our knowledge, and includes the greater part of what Perrine regarded as
rills. After the block had been prepared the author added a western continua-
tion of the Perrine-rill, three crater-like enlargements, another branch of the
rill toward the north-east border, and a pit at the eastern end of the broad floor
of the valley, so that the American discovery is now fully confirmed
at Landscuhl.

126

THE MOON

failed to close again toward the eastern end, partly
on account of displacement and partly on account of
being stopped up with debris, and the difference in
specific gravity of the solidified and the liquid matter
prevented the halves of the mass from sinking down
to the level of the fluid, which was also hindered on
the east by the fragments pressing underneath them.
The Carpathian hills also exhibit elevated surfaces,

IPP

Fig. 53. Fauth's map of the valley of the Alps (1 mm.=960 m )

THE MOON 127

steep bluffs, and broken edge$ on the Mare-side ; inland
we see hilly debris scattered loosely and wide around.

There are some instances of even greater elevations
of mountain-masses. The Apennines seem to exhibit
this formation, and also, the Caucasus. But when we
examine them in good light they are merely regions
in which the parts fail to be connected, or are only
connected by secondary hills. The general level of
the moon appears throughout, and forms what we call
the valley or the plain on earth, though on the moon
it would be more correct to call it the common basis
of the heights, often only seen as a space between
them. We can learn from a further instance on our
satellite how we may picture to ourselves this catas-
trophe of the forcing upwards of parts of its shell. The
comparatively small Mare nectaris is encircled in a
wide circle by the seemingly gigantic parallel lines of
the Altai mountains, with an inner fall from Piccolomini
to Tacitus, though the expert can trace it much further.
Here one can almost see at a glance that the whole of
the inner surface subsided at one time or other, and —
relatively to lunar dimensions — remained at a slightly
lower level. Was it the same process in the Mare
imbrium ? Was it the case with the Mare serenitatis —
with the ' seas ' generally ? Yes and no. The seas in
general are flat, because they have remained flooded.
The first inundation from below has, however, been
followed by others in the Mare nectaris, and this has
given it its actual character. We may extend the
principle with the necessary reserves and enlargements
to other objects. The transition to Grimaldi, Clavius,
and similar gigantic walled plains is obvious ; but it
will not be easy to say where ' eruptions ' must be
substituted for depressions in order to explain the
plastic features of the moon's surface.

There are still two very distinctive and therefore
important lunar forms that we commend to the notice

Fig. 54. The Mare nectaris, and the regions to the north of it.
(Cf. figs. 9 and 33.)

THE MOON 1291

of the reader who has a good map of the moon or a
telescope. These are the isolated plateaux and moun-
tains. A few of the chief examples of the former ar?> :
a mass with many inequalities and depressions to the'
north of Copernicus and the west of Gay Lussac ; ai
still more sharply defined mountainous mass to the
north of Euclides, quite distinct from Riphteus and
rising out of the mare with a smooth border ; an
equally large mass to the north-west of Fra Mauro,
which has clearly been broken from its wall and forced
to one side ; a large triangular island to the east of
Hippalus in the Mare humor am, and many others.
The common features of them are that they emerge
sharply from the smooth plain and are quite separated;
from the neighbouring heights. They look like plates*
laid on the ground, or rather, like flat islands embedded;
in a fluid and solidifying in it.

When we turn to consider the size of these parts,
of mountains, we find some that have more resemblance:
to groups of hills, such as the Harbinger mountains
in the Sinus iridum, or the long lines to the south-east
of Plato. We might also adduce the scattered plateaux
and mountains to the south of Archimedes or the.
southern end of Caucusus, and other similar structures.*
But we shall see the character of these elevations
more strikingly if we take them in the following ordet :
The mountains to the north-west of Aristarchus, Pico
and Piton on Plato, Lahire, to the east and the peak,
to the west of Lambert, and others (see figs. 21-27;
and 47-51). In these cases a single peak, or a mountain
split into several peaks, rises straight up, and casts
enormous shadows at the rising or setting of the sun.
Some of the central mountains inside the large ring*
formations are of the same character. We must not,
of course, trust the superficial appearance too closely,
because, in spite of their remarkably pointed shadows^
all these ' peaks ' are really very flat, as the following
i

130 THE MOON

figures will show. Pico is 12-15 miles broad at its
base, and rises to a height of 2,676 yards, so that the
proportion of height to width at the foot is 1 : 8 or 1 :
10 ; Piton, 15 miles in breadth and 2,333 yards high,
has a proportion of 1 : 12 ; Lahire, 1,611 yards high
and 11 miles wide, has a proportion of 1 : 12*4 ; and
the peak Gamma, on Lambert, is 1,166 yards high and
less than four miles broad, and so has a proportion of
about 1 : 6. The sharply defined uplands and the
isolated peaks with their white tint look to us as if
they once floated in a fluid, with the greater part of
their mass below the surface, and then with the
solidification of the sea only showed their upper parts
above the surface. The whole of the lunar Alps
consists of peaks of this kind, and they are relics of
the mass that lies in the fluid below.

We will now consider a last category of lunar
features that are often found on the map, and still
more frequently on the moon itself, and that will give
us a new light on the solidity of the material of our
satellite. . These are the breaches, clefts, or * rills.'
They have nothing in common with river-courses or
anything of that description. They are quickly recog-
nised by the practised eye on account of their reversed
relief . Whilst the heights are bright on the side that
lies nearest the sun, and dark on the opposite side, it
is, of course, just the reverse with depressions. The
rills may, it is true, run in such an unfavourable direc-
tion as regards the sun's rays that they show hardly
any trace of light and shade ; in that case one needs
prolonged research before forming an opinion as to
their real nature. They have been compared to
terrestrial gorges, to the valley of the Rhine between
Bingen and Coblenz, to ravines like the Via mala, or
to the canons of Colorado. But, on the strength of
an acquaintance with several hundreds of well-placed
rills we hold that these comparisons are quite unjustified

THE MOON 131

especially when they are based closely on the apparent
features, which are so deceptive on the moon. If we
take the Rhine-valley below Coblenz and the whole
plain of the upper Rhine as extremes, taking account
of both depression and flatness, no doubt the lunar
rills will come somewhere between the two. Whether
the finest of the rills in the moon's shell are still steeper
and deeper we cannot say ; we are fortunate to
perceive them at all.

There are, however, two quite distinct types, the
flat and broad rills, and the narrow ones that we can
hardly tell the depth of. The ' great valley ' near
Herodotus and the ' valley of the Alps ' are the largest
and earliest known of these objects. There are also
the 200-mile long rill of Ariadseus, the Hyginus-rill,
the wide canal at the foot of Plinius, the three chief
rills near Hippalus, the 170-mile long cleft between
Hesiodus and Capuanus, the great valley inside
Petavius, etc. The narrow ones are the most numerous,-
they are sometimes very long, sometimes short, like
fine cracks. The system of rills about Triesnecker,
the clefts in Posidonius, Gassendi, and Ramsden, are
so many examples. What makes the rills so interesting
from the selenological point <Sf view is that they so
often make their appearance round areas of subsidence
or inside them (Gassendi ?). It is evident that this phe-
nomenon has occurred round the borders of the Mare
humorum and the Mare serenitatis. Where they seem
to be lacking, we find a cognate structure, the long and
flat mountain-veins, which are clear signs of earlier
cleavage-lines in the Maria serenitatis, humorum, and
hectaris, they run more or less parallel to the shores.
Further, the ranges of hills that run in bold, S-shaped, flat
curves from the ring-mountain Lambert towards the
south-west, north, and north-east, are nothing more than
earlier ruptures, filled up to overflow with a fluid that
issued from below and solidified. In this case we

Fig. 55. Map of the ring- mountain Gassendi, by Ph. Fauth
(1 mm =940 m.)

THE MOON 133

willingly endorse the Meydenbauer-Thiersch theory of
meteoric impact, which may have beeri the cause of the*
bursting of the moon's shell. Since Prof. Prinz proved*
by many experiments and illustrations the reality of
the apparent features, and showed that brittle masses
split generally in three different directions at the place
of impact or of least resistance, the frequent occurrence
of three rays on the mountain- veins and the frequent
triangular and hexagonal form of the ring-structures
(Godin, Ptolemseus, and many others) are no longer
very puzzling. Rills must generally be regarded as
secondary and subsidiary formations, and they help us
to appreciate the brittleness of the solid matter of the
moon.

In this connection it would not be out of place to
recall the abrupt gradation of the plains, as we find in
Thebit, where it is known as ' the long wall ' (78 miles)
or (in England) * the railway.' The steep fall lies toward
the east, so that it only casts shadows in the first quarter
of the moon. The author has on careful examination,
recognised at the foot of the wall the line of rupture and
some remarkable details ; Gaudibert also detected the
rupture. There is a similar case on the western edge
of the chief rill near Cauchy, and something like it,
though without a rill, is seen to the west of Cassini.
In order to appreciate these details we must carefully
bear in mind what we saw above as to the possible
origin of these terraced falls.

We have already observed that the broader
valleys were the first to be discovered. Schroeter
found 1 1 rills, and with the improvement of the
achromatic telescope and of our knowledge of the
character of the rills the number increased. Madler
has indicated 77 of them ; Lohrmann, with rather
better instruments, 99 ;|^Schmidt gives on his map [no

* Esquisses 8&6rwlogique8. See also his L'6eh°Me riduite des experiences
gtologiques.

134 THE MOON

less than 348 of these very elusive objects. Schmidt
did not think the number was exhaustive, and conjec-
tured that they would prove to be about 500. His
successors have added a few, though there was little
choice in reproducing them. Gaudibert gives 324
(partly new ones) on his map of 1885, and Neison gave
366 in 1881. But we shall only get reliable and very
desirable information about the number of the rills in
particular, and the centres of rupture in general, from
some such study of the moon's topography as L.
Brenner is making, in small tracts, at Lussinpiccolo,
where some 360 new rills have been discovered, or as
the author is making on a larger scale with the object
of producing a map 11 feet in diameter. The author
has discovered a further 1,258 rills in a small portion
of the moon's surface, and these make up 1,600 with
Schmidt's indications.

135

CHAPTER VI

Some Conclusions

From what we have now seen the reader will
understand how difficult it is to penetrate the mysteries
of lunar processes, and it will seem, at first sight, very-
remarkable that we should speak at all about air and
water on this distant body. Here, however, we are
assisted by our knowledge of the physical properties
of fluid, which are unchanged even in the very singular
circumstances of the moon ; these are the refraction
of light and evaporation. A lunar atmosphere in the
remotest degree like ours in extent would have revealed
itself on the moon long ago by rendering deep cavities
vaguer, by toning down the blackness of shadows and
the outlines of thingsj and by causing a very perceptible
twilight. Moreover, the aqueous vapour which would
then certainly be present would become visible in the
form, of mists or clouds, especially at the very spots
where we find details quite devoid of haziness and
wonderfully clear — on the terminator. We must also
remember that water-surfaces of even moderate extent
would be directly visible. Some of the communications
of earlier observers, which must be taken with reserve,
related the discovery, in certain cases, of a nebulous
haziness or traces of a twilight at certain points. These
are not strong enough to survive the objection that
arises from the well-known imperfection of their
lenses ; and there is a certain sort of twilight, as the

136 THE MOON

author knows from his own experience, that can be
explained without any atmosphere. Haziness of one
kind or other can be found very clearly any month,
namely, when the sun has passed over brilliant- white
and deep crater-plains. Thus we see the sun-lit
interior of the deep Theophilus, Tycho, or Copernicus,
entirely lost in light, and even the experienced eye
finds it very difficult to recognise degrees of brightness
within the brilliant part. On the other hand, it is
well-known that many large structures cannot be
detected in the full moon, or rather, at the time when
the sun's rays are almost vertical, even if the localities
are quite familiar. We will return to this fact later
on, and make a closer study of it.

However, all these tests are very coarse in com-
parison with the investigation of the refractive power
of an atmospheric envelope. The comparatively large
disk of the moon passes over a number of bright fixed
Stars in the course of its monthly tour of the heavens.
They disappear at its left limb, and reappear at the
right. We know from physical experiments that an
atmospheric mantle refracts the light of the stars, so
that a star seems to remain for some time on the edge
of a cosmic body after we know it has been really
occulted (or eclipsed), and that it seems to be delayed ?
for a time in making its appearance at the other edge,
though we know it has passed the edge. Now we have
calculated the ' occupations ' of a number of stars from
their known positions in the heavens and the pretty
accurately known diameter of the moon, and we find
no ground for supposing that the moon was under-rated
in measurement owing to a refraction of the light of
the stars ; we discovered no trace of a departure of
its body from the circular form, or of what we call
flattening in the other planets.

The test is, therefore, so far conclusive ; and if
careful experts still, taking all considerations into

THE MOON 137

account, speak of an atmosphere 300 times (Neison)
or 1,000 times (Bessel) thinner than our own, there are
several ways in which we may philosophically examine
the result of their calculations. In the first place this
tenuity would amount in the deepest cavities on the
moon to a barometrical pressure of from 2 to 0'75 mm.,
which is equivalent to what is called the vacuum under
the glass bell of an air-pump ; in the second place it
seems as if some experts are straining the evidence to
retain an atmosphere at all costs on the moon, because
they take their stand on the plutonic theory of its
origin, and this involves the formation of a gaseous
mantle about the cooled globe.

Johnston Stoney has lately communicated an
important piece of knowledge in regard to the assumed
atmospheres on various large cosmic bodies. It has been
shown that the earth cannot retain free hydrogen and
helium permanently in its atmosphere, and that
aqueous vapour cannot be found permanently in the
atmospheres of Mercury and Mars. Probably none of
the moons in our planetary system, except perhaps
that of Neptune, has a relatively thick atmosphere.
In our moon the expansive property of the gases
preponderates so much over gravitation that any
atmospheric mantle must have been dissipated into
space long ago. Finally, it will follow from our
subsequent positions that we can, for a fresh reason,
dispense with this atmospheric mantle, and in fact
show that there probably never was such a thing on
the moon. We will only add that the finest tests,
including the eclipsing of Jupiter, Saturn, and the sun
by the moon, confirm the absence of a lunar atmosphere.

How does the matter stand as regards water?
Any man who is well acquainted with its physical, and
especially its thermodynamical properties, will know
that it cannot exist where there is no air. At the sea-
level water must be raised to a temperature of 100° C.

138 THE MOON

for it to boil ; on a moderately high mountain-summit
it boils at 95° C, in conditions that correspond to a
barometrical pressure of 640-630 mm. The less the
pressure exerted on the surface of the water, the less
heat is required to bring it to the boiling point ; under
the bell of an air-pump it does not need to be hot at all,
and will even boil at a temperature of 0°. Hence on
the air-less moon ice-cold water would boil. In other
words, there cannot be any fluid water on the moon.

But the lack of air leads to another and more
important feature. We know that the thicker layer
of the atmosphere on the level ground amounts to a
sort of reservoir for the solar radiation, which is con-
verted from light into heat. On the summits of the
Alps, or at a great height in a balloon, the air can no
longer retain this heat, so that ice and snow remain
unmelted in spite of an increased solar radiation in
the purer air, that burns the skin. If we go a step
further in imagination, and fancy ourselves at the
indefinable limit of the atmosphere, we shall be exposed
to the unmitigated ardour of the sun, yet surrounded
on all sides by the appalling cold of space. This cold,
the so-called absolute zero, lies 273° C. below the
freezing point of water. Now, as the moon has no
atmosphere, there will be no mitigation of radiation,
or storing up of heat on it, and its surface must possess
in the highest degree the conditions of our loftiest,
glacier-covered peaks. The moon is covered with a
thick layer of ice 9 and exposed to the intense cold of
space— 273° C.

Nearly twenty years ago a similar conclusion to
this was reached by Dr. P. Andries (Sirius, 1887, VII).
According to Langley's observations with the Violle
actinometer, as amended by him, the solar radiation
on Mount Whitny (3,935 yards high) was 31" 7° C.
$bove the temperature of empty space (in vacuo), and

THE MOON 139

Violle found a difference of 29*8 C. on Mont Blanc
(5,344 yards). When we take into account the real
value of the * solar constant ' (the amount of heat that
the real solar radiation communicates to 1 com. of
water in one minute) these figures go up to about 48° C.
The basic temperature in the moon must be only
-273°C, and its surface cannot, in the best con-
ditions, rise above -225° C. Ericson suggested the
complete glaciation of the moon in Nature (vol. 34,
No. 827) before Andries did so, and gave an explanation
of lunar forms on these lines that differs in many
respects from that of Andries. Lord Rosse was
enabled by his measurements to appreciate the differ-
ences in temperature on the moon's surface during full
radiation and by night, and found them to be over
300° C. But the temperatures cannot be determined
with any accuracy. Lord Rosse's results have often
been questioned, but they are supported by the recent
investigations of Very. Very believes that at the
moon's equator, when the sun is at its highest, the
ground increases its temperature by more than 100° C.
(which would be- 173° C.). When the solar radiation
ceases the temperature must fall enormously, and
probably approach that of space, which is believed to
be- 273° C (Newcomb).

The objection will be raised, of course, that if the
moon has no water, it cannot have any ice. The
objection is quite wrong. Ice is certainly the same
material as water ; but the matter that we express by
the chemical formula H 2 0, may exist either in the
form of solid ice or of gaseous vapour, in conditions
where the liquid state is impossible because the degrees
between freezing and boiling point are not found.
Many terrestrial phenomena, especially the dreaded
heavy hail-storms with blocks of ice 4 inches thick,
which still puzzle meteorologists, point to an accession
of ice from outer_ space ; and the moon with its coati

140 THE MOON

•of pure ice is an eloquent witness to the existence of
ice in the solar system.

We now come to the question of colour. Aris-
tarchus and various other spots on the moon are lit up
so strongly, almost to a pure white, in the solar rays,
that even the seasoned eye of an experienced observer
is dazed by it, and the inexperienced observer feels
pain. Other landscapes look as if they are covered
with hoar-frost. Most of them bleach very visibly,
forming and depositing a light hoar-frost during the
14-day lunar ' day,' and are dull when they pass away
into the lunar night. No material exposed to sun-
light shows a similar change of colour, so as to be
visible even in the dark. In certain circumstances,
which we cannot explain in detail in the present brief
survey, the surface may be darkened instead of
Meached ; it is very remarkable that the deep and
isolated circle of Plato has often been made a subject
of investigation in this respect*. But the finest
indication is the brightness, claimed by the author to
be hoar-frost, and increasing with the height of the
sun on the crests of the ring-walls, ridges, and moun-
tains, that reflects the strongest light when the radiation
is almost vertical, and grows darker as the sun sinks.
Many observers, like Majert, think they see the ' snow
line ' or glacial cap on these peaks, and it is an obser-
vation that can be repeated in hundreds of instances.
If others have, like the author, seen unillumined parts
of ring-mountains glow as if in a faint twilight, this
must have been due to earth-light, often in conjunction

♦See pamphlet of W. R. Birt, 1869, another in 1873. Also Neison, The
Moon, p. 172 : Siriux, 1887, VII (article of Stanley Williams on Plato) : Sirim,
1901, VIII (article on 'Pickering's observations of Plato.') The author's
observations of the colour of the interior of Plato, which were greatly enhanced
on March 6 and 7, 1906, go farther than any other in this department. The
map given (Fig. 34) shows this. It must be taken as a general survey, as the
visibility of particular details depends on the height of the sun above 1 Plato.
The work of showing the ring-mountain in the various phases of illumination
yet remains to be done.

THE MOON 141

with the reflection of sun-light from illumined walls-
into the lunar night, or at the close of the 14-days'
radiation, which may have caused a phosphorescence
or luminescence, as has often been observed on glaciers
(so Professor Maurer, of Zurich, informs me).

The blackish spots we described in a previous-
chapter are just as easily explained if we regard them
as pure ice. Ice naturally assumes a crystalline and
transparent form, as can be seen in any pond. Why
these interesting localities do not engender hoar-frost
under the 14-days ardour of the sun, as the other
parts of the moon's shell, consisting of amorphous
white ice, do, may be explained by the fact that smooth
surfaces reflect light almost as well as a mirror, and
change very little under the action of heat, and so do
not form hoar.

Eyes that are sensitive to colour have discovered
on the moon regions of every shade of white from
yellow and gray to black, as well as greenish and faintly
reddish localities. But if wide stretches of the earth's
surface may be tinted by meteoric (ferruginous) dust,
where atmospheric influences are constantly changing
and weakening the colour, it will be much easier for
traces of this kind to remain visible on the moon. Here
again we may have recourse to the meteoric hypothesis,
and regard the meteors, which occasioned the breaches
and overflows that we now look upon as ' seas,' as the
causes of the colouring of this- or that Mare. The
shell of the moon must have a mantle of ice ; but
underneath this, there is, perhaps, an ocean, the wavea
of which, have at times, broken through or been
pressed through the ice. The mass of water, however,
could not rush out in an explosive vapour, because
there was no air to take it up and convey it. Thi&
breaking of the icy shell would probably take place
with massive effects on the intensely cold surface, and
the fact of the repetition of the catastrophe enables

142 THE MOON

us to understand the overflows that we call * seas ' and
the gradual construction of the remarkably flat walled
plains with hollow, interior, which would be washed
out, so to say, by the. ebb and flow of warmer water
from below. Lakes of water in depressions of that
kind evaporate freely before the freezing or the retreat
inwards of the overflow. This vapour must be frozen
into ice-dust immediately after its formation ; and
the longer and more frequently the hollow is filled
with the water in its ebb and flow, the more would
this vapour, turned into a cloud of ice-powder, be
pressed out by its own weight through holes and
passes in the encircling wall. Here it would not be
blown to either side by currents of air, and would
gradually sink outwards, and cover the district round
with radial streaks. Thus we would get a corona of
rays ! The formation of such very long streaks in
some circumstances by the ice-dust may be explained
by the persistence of the phenomenon and the slight
gravitational influence of the moon on the icy particles.

These suggestions as to how the glacial character
of the moon's shell will enable us to solve its greatest
problems are all that we need give here. We may
now point out that we are calling into question only
the plutonic theory of the moon's surface, not of the
moon itself. Its nucleus, the real body of the moon,
which we look upon as covered with the ocean we
have suggested, must lie in it like the yolk in the white
of an egg. If we assume for this globular nucleus —
which we take, on terrestrial analogy, to be metallic-
earthy — an average specific gravity of 4 * 5 (the earth's
is 5 # 5), we need, as a very simple calculation will show,
an ocean 115 miles deep (or a round water-shell of
this thickness) in order to give the well-known average
gravity of 3 '5.

We will say just a few words on the remarkable
consequences oi this theory. The cosmic rain of ice,

THE MOON 143

of which we have previously pointed out one trace,
must have acted forages on the smaller moon of former
times, even when it was in the period of incandescence
and must have gradually brought it-' under water.'
From this point of view we can understand that the
enclosed and isolated nucleus would, in consequence
of the ever-increasing hydrostatic pressure, not be in
a position to evolve gases at its surface from its mineral
interior, and so the moon would have no atmosphere.
Its ocean naturally accumulated more on the tidal
side facing the earth, and formed a huge tidal mountain
on that side ; on this account the nucleus must be
eccentric, or displaced toward the other side, and so
those astronomers are right who place the centre of
gravity of our satellite beyond the absolute centre of
the sphere*.

Dr. Mainka, also, is right when, on very careful
measurement, he can find no trace of the suggested
oval curve of the moon's surface in the direction of
the earth. The tidal mountain, which remained on
the side turned toward the earth, was bound to alter
by friction the original rotation of the moon, and
thus we get the present situation of relative rest, and
the moon only rotates once in the course of its four-
week revolution.

These are a few instances showing how questions
as to the appearance, light and colour variations,
specific gravity, centre of gravity, and shape of the
moon are readily answered if this theory of a complete
glaciation of the surface of our planet, which we will
establish further in some future work, is made the
base of lunar exploration.

We cannot conclude our historical account of
lunar science without saying a few words about the

*See Prof. Franz, Ueber die Figur den Monde* (1900); Dr. Mainka,
Untersuchung iiber die Verldngerung des Mond&i nach der Erde zu (1901). Cf.
also Neison, p. 12.

144 THE MOON

\rhanges ' which various observers have tried to
prove on the moon during the last hundred years. We
will not deal with Schroeter's fantastic expectations
or Gruithuisen's precarious speculations — such as his
discovery of an 4 artificial wall ' to the north of the
ring-mountain Schroeter. Madler, who had great
authority in this direction, was more than reserved in
regard to their ideas. Later on comparisons were
made between Madler and Lohrmann's and Schmidt's
maps, and from certain discrepancies here and there
it was concluded that there had been real changes in
lunar objects. But a few examples will show that the
first accomplishments in selenography, though they
brought an immense amount of fresh detail into the
science, were bound to suffer from many omissions
and other defects. Indeed, we cannot directly compare
our present topographical knowledge with that of
our predecessors, who had to acquire very laboriously
the information that we gather so easily to-day from
maps and photographs.

The defects of the earlier exploration, the instru-
ments and magnification employed, and possibly the
influence of suggestion, can be seen very well in
Madler's repeated study of the small craters Messier
and Messier A. He thought that they were absolutely
alike in detail, and reproduced them as simple ellipses.
Schmidt then wrote an exhaustive monograph at
Athens, and gave them a characteristic form — also
indicated by Lohrmann — on the map, yet we find
them reproduced on Klein's map (1884) in the older
and inaccurate version of Madler. We may add that
Gruithuisen had given a more correct presentation of
their size and shape in 1824. To-day the craters are
as different as possible. A peculiarity in the eastern
wall was first discovered by Schmidt, and since then
the author has detected many interesting details, as
will be seen on the map we have given. The original

THE MOON

145

map is on a scale of 1 : 200,000, or half the size of
the new German national map.

The question of ' changes ' first came to the front
when Schmidt in 1866, failed to find the crater Linne
indicated on the older maps. It at once excited a
heated controversy, the only useful result of which
was that at last a large number of astronomers — not
very expert in lunar exploration, it must be said —

Fig. 56
Map of the crater Messier and A, by Ph. Fauth (1 mm.= 650 m.)

146

THE MOON

were induced to turn their large telescopes on the
object, and so a number of finer features were detected.
We know these details much better to-day than the
plan shows ; but the older communications show
quite plainly that there cannot have been any change
in the object. We can now say confidently that
Schmidt contended much too rashly and obstinately
for a change. Klein, it is true, refers us to Madler's
original drawings, which he has studied, but one can
gather as little from this as we could in the case of
the Messier crater and the Hyginus cavity. We have
every reason to know that Madler and Lohrmann were
deceived, and that Linne never looked different from
what it does to-day.

Fig. 57
Plan of region round Linne, by Ph. Fauth (1 mm = 450= 450 m.)

THE MOON 147

The question is not yet abandoned, but it may
be said that the whole literature of the supposed
changes in the last forty years turns on Schmidt's
fateful conclusion. Professor Prinz and L. Brenner
have made more extensive investigations of the
object*. Among the many opinions expressed on
the subject in the last few years we will quote only
three, as in these cases powerful instruments were
employed. In the first place Professor Pickering
noticed at Arequipa (1897-8) changes of size in the
white spot of Linne (see note, page 42), which is given
in punctuated lines on our chart. The spot was large
when it emerged from the night, decreased rapidly
until a day after greatest illumination, and then
slowly regained its proportions ; and during the
eclipse of the moon on October 16, 1902, the diameter
increased in the shadow. The same thing was observed
by Dr. Wirtz with the Strassburg 18-inch telescope
during the eclipse of April 11, 1903. Professor
Becker rightly remarked that there was probably a
fault in the observation, and we may support his
objection with the following explanation: — At first
Linne was probably measured too small in the glaring
light, as the unseasoned eye of the observer would
sustain some strain, and the spot is not very sharply
defined. When the light diminished in the eclipse,
and the eye had grown accustomed to the milder tones,
the dim outline of the spot was measured again, and
larger dimensions were found. An eye that is less
sensitive to lunar light can trace the outline of the
white spot at other times, n Now^Dr.lWirtz has made

* See Prinz in del et Terre, 1903, ix : ' y a-t-il eu des changements dans
les crateres lunaires Messier et Linne ? ' Also Sirius, 1877, viii, for Schroeter's
observations ; and Sirius, 1893, xii. Brenner writes in the Naturw. Wochenschrift
on * Changes in the Moon,' and in the Astr. Rundschau (no. 71) on * The crater
Linne.' See also Fauth * Linne and lunar changes ' in the Astr. Rundschau
(no. 73), and in Sirius, 1877, v and vi : also Klein's Durchmusterung (p. 160),
and article in Sirius, 1884, iii (with map), and Schmidt's Ueberdie Mondlandschafl
Messier, 1882.

148

THE MOON

continued measurements of it during a lunation, and
found that 4 the diameter of Linne varies in the course
of a lunation, and the formula is that, after a lunar
day has begun for it, at about the seventh day of the
moon's age, it increases about 116 yards each succeeding
day, until it passes into the night again, when the
moon is about twenty-one days old.' This formula
must be taken with great reserve.

Professor E. E. Barnard has discussed a number
of measurements of Linne taken with the 40-inch
telescope at the Yerkes Observatory from December,
1902, to November, 1904, and found surprisingly little
of interest in them (see note, page 42). In general,
he believes that the spot decreases as the illumination
increases, and is reduced to nearly half its diameter

Fig. 58
Chart of the region about Alpetragius, by Ph. Fauth (1 mm.=460 m.)

THE MOON 149

in a strong light. Professor Pickering has attributed
this change to a deposit of hoar-frost, and we can thus
welcome his explanation as a support of our theory
of the icy character especially of the white spots on
the moon. No progress has been made in determining
the topography of Linne beyond the chart given here,
but the question is whether there has been any change
in the crater. We do not believe there has. We may
add that Madler made the same topographical mistake
in two other cases (Parry B and Alpetragius D) ; he
thought there was reason to regard white spots as flat
craters. Lohrmann avoided that mistake, but fell
into others in describing flat mountain-tops as the
craters. In this respect it is noteworthy that Schmidt,
startled by the threefold repetition of the case, only
expended his zeal on Linne, and not on the other quite
analogous cases. He must have felt himself that he
had gone too far in the first case.

The progress of lunar research has taught us that
we cannot swear to any single one of the thousands
of details on the early maps: Even Schmidt's map,
which was completed fifty years later, has serious
defects here and there. The present author himself has
had to strike out a 12 mile wide crater ( ' Melloni,'
section XIX), which does not exist at all. And on
testing the two older maps, we found the following
surprising results : — On half the surface of the map
(not counting the chaotic mountainous districts)
for instance, to the south, and without the border
districts) Madler has omitted 17 craters of such dimen-
sions that they ought not to have escaped him ; and
on the other hand, he gives 337 pits and small crater-
structures that are not found on the moon at all. We
can easily recognise Madler's conscientiousness in
taking white spots for craters. Lohrmann also has
not seen many craters that were certainly within the
range of his telescope, and given 95 craters that did

150

THE MOON

not exist. These instances warn us not to draw
general conclusions from the small crater-forms given
on these two maps.

Further support to the theory of physical changes
was found in the groups of rills on Aristarchus and
Ramsden. The author, who has prepared two exhaus-
tive maps of these, and has spent 21 years in lunar
observation, can only express his surprise that any
changes or ' disturbances ' were claimed here. At
Landstuhl there has never been any ambiguity about
the details. The idea of the possibility of extensive
changes in the appearance has sometimes occasioned
the most curious results. Specialists announced, for
instance, that Lohrmann's great gray spiral structure
in Triesnecker, had disappeared ; yet one can see it
well enough in any moderately successful photograph,
and it is perfectly clear with the telescope in a good
light. The blackish spots in Alphonsus are supposed
to have changed ; as if there had ever been any special
attention paid to them. Even Dr. Klein's special map
(Sirius, 1882, IX) shows how little people expected in

Fig. 59
Pickering's map.

Fig. 60
Fauth's map.

The dark spots in Alphonsus.

THE MOON 151

these things formerly (compare our maps in Figs 42
and 43). In further illustration of our point we may
take Pickering's and the author's reproduction of the
Alphonsus spots. Two darkly outlined small craters
in the Mare nectaris could not have been overlooked
by Madler and Lohrmann, it. is said ; as if the former
had not overlooked 17 others, and the latter had not
indicated a cavity at the very spots ! They did not
look for dark spots, nor are the craters in question of
such a nature that they would be likely to catch the
eye of early observers. From Schroeter and Gruithuisen
we have nothing to expect in this direction. In the
same way a number of novelties of more considerable
dimensions have been signalised at different places.
They haye proved quite groundless and can generally
be traced to the observer's unfamiliarity with lunar
matters.

We repeat that if lunar experts had not been
stimulated by the futile problems of Messier and Linne,
many of the more recent statements about other
localities, particularly about the region of Hyginus,
near the centre of the moon, would have had a cooler
and more judicious reception. There is not only the
cavity, Hyginus N, first announced by Klein in 1877,
but also a broad flat valley (between the Schneckenberg
and the crater of Hyginus), 19 miles long and two miles
wide, and between the two a very small crater,
6 Hyginus N 1,' according to Krieger, and a group of
8 or 10 very small pits in the vicinity, in which Brenner
found changes. In view of the obstinacy with which
' Hyginus N ' has for nearly 30 years been maintained
to be a new formation, it is advisable to emphasize
the fact that the deep shadows of the cavity are due
entirely to its western edge with a longish dome, that
the so-called ' crater ' only has the appearance of a
cavity at sunset, and that Madler himself described
the dome, the cause of the ' black crater,' and the

152

THE MOON

Figs. 61-63

The region of Hyginus. Sections of Madler's and Lohrmann's inaps
(natural size.) Klein's map (slightly enlarged.)

crater lying between it and Hyginus (describing the
latter as a hill) ; he also clearly reproduced the ele-
vations to the west of the latter in the form of a
longish hill, as correctly as was possible with his
instrument.* Lohrmann, again, has reproduced with
great fidelity the district to the west of ' N,' and
especially the hill in question. If we suppose, as we
are entitled to do, that both these older masters
recognised the hill as casting a shadow, and they
needed only a single observation at sunset to convince
themselves that the cavity is not dark then, and that
the eastern appendage of the hill shines white — they
would not have had the least occasion to give a crater
on their maps. A hill was quite enough— and a hill
they gave.

*Cf. Rand Capron's remarks in Sirius, 1886, i, where he wrongly describes
this hill (crater ?) as Hyginus N. Klein speaks in the same periodical of the
details of Madler's map, which he certainly could not identify. The hill in
question is the larger crater to the east, marked 78 on Brenner's map (Naturw.
Wochenschrifb, 1896, x). Cf. also Sirins, 1879, iv, where Klein speaks of sketches
made with Lord Lindsay's 15-inch. * In the second sketch one recognises a hill
there,' he says. Neison says \Sirius, 1879, vi) : * there was no trace of a bright
edge ; ' and in regard to a drawing of Edgcomb's, who had observed with a
9-3 inch like himself, he says : 'there was no wall to be seen.' Klein further
remarks : * some English observers have pointed to the fact that the new object
N in Hyginus is not a crater, but a concave depression, or a spoon-shaped
marking of the ground.' In Sirius, 1893, i, Roger Sprague declared N to be a
shadow of the western hill, which is in part correct.

Fig. 64
Map of the Hyginus region, by Ph. Fauth (1 mm.= 1,050 m.)

154 THE MOON

As to the lfti'ge valley near Hyginus, that is plain
at sunset, but soon becomes invisible ; it is said that
Gruithuisen's observations make it clear that he must
have seen it and reproduced it especially on November
28, 1824, at 5.30 in the evening, if it had then been
visible. In order to study the matter properly the
author has used 36 drawings with the shadows, in
addition to his own observations, and compared with
them Gruithuisen's drawing, taken when the terminator
was 1° to the east. The result was as follows. In the
first place at this stage of illumination the valley is
only vaguely, and not definitely, shadowed ; in the
second place, on Gruithuisen's drawing, which was
only made for the sake of the finer rill of Triesnecker
and two fine ' circlets,' this object comes on the extreme
left, and actually touches the edge of the drawing.
Klein's comparative sketch is incorrect in the position
of the valley, in blackness and in the distance of
the valley from the edge of the paper. It is thus
clear that Klein has failed in his proof. That Gruit-
huisen, moreover, was not too accurate in things that
he did not wish to emphasise is clear from the omission
of the shadows in the craters A and B, and the mountain
to the north of them, though even these are well
characterised and much easier to recognise than the
' circlets.' They were not recognised by Krieger with
a 10-inch refractor. Schmidt himself, who drew the
valley on February 18, 1869 (Sims, 1882, 1), and added
further details on March 28, 1871, overlooked it on
June 5, 1870, and December 7, 1872, when it was
particularly visible. On June 5, 1889, V. Nielsen
discovered a flat pit, running from the cavity * N '
toward the valley on the south-east, and this is omitted
on four drawings by Stuyvaerts and those of observers
generally. The author was the second to notice it,
on March 17, 1891, during his fourth or fifth observation
of the Hyginus region — the 6J inch refractor had only

JH 11 %i "Mm,, m

!> Si „ %t# v «f|

156 THE MOON

been established nine months — and it is really an
easy object. Yet Krieger made a drawing of the
district on April 12, 1894 (Atlas of the Moon, PL 8),
with a 10-inch telescope and powers of 175 and 520,
and failed to see this easy depression. We must
conclude that there has not been sufficient discrimi-
nation, and that new foundations have been assumed
too readily. The belief in these changes in the Hyginus
region seemed to be a better position than the belief
in a collapse of the ' former ' Linne, and so the author
thought it well to enter more closely into the matter.
Students may be invited to consider the details within
the cavity, as we give them on Fig. 65.

The object N also is not a new formation. It
was given by the author on a special map in July,
1893, and afterwards claimed by Krieger to be a ' new
structure.' The pits which Brenner regards as newly-
formed are objects of such delicacy that it took all
the work of that observer and the present writer to
establish their existence. The very fact that these
and others have only been gradually detected shows
that with practice and perseverance we may discover
many things still in the middle of ' known localities,'
yet they will not be * new formations.'

The author has no wish to enforce his view of
these things on other selenographers ; but as a student
of the moon for the last 20 years, and as probably one
of the few living investigators who have kept in practical
touch with the results of selenography, he is bound
to express his conviction that no eye has ever seen a
physical change in the plastic features of the moon's
surface.

It is fortunate that the investigation of ' changes '
has been directed in another direction, namely, to
the study of the alterations of light and colour that
recur in almost the same way every month. This is
the proper quarter for enquiry. Besides the particular

THE MOOT* 157

works we have mentioned on certain dark spots,
there are earlier and recent researches on the plain of
Plato and the interior of Alphonus ; we have already
given illustrations of these. In addition, Professor
Pickering has made the characteristic ring-mountain
Eratosthenes the subject of a searching enquiry, and
has published pictures of it with which we must
deal briefly*. The evil star that has ruled lunar
observation in a transitional period has wrought its
mischief here also. In a word, it is improper to speak
of the lines and spots that Pickering saw on the walls
and in the vicinity of Eratosthenes during the advance
of the illumination as ' canals ' and ' seas.' These
ideas have introduced error enough in the case of Mars.
We may say, in fact, that the object depicted by
Pickering does not exist in that form. The American
astronomer only shows that he has approached a
difficult task without proper preparation, and that
he is not well acquainted with the topography of the
ring-mountain. The details he gives are sometimes so
sharp that they are found on moderate photographs.

There is not much to be done on negative grounds,
without positive proof. On this account we have
commenced a series of observations of brightness on
the basis of a thorough topographical detail-map, and
in the course of 1906 we intend to reproduce the light-
tones during a whole lunation, in order to prove to
those who are interested what the real nature of these
mysterious new formations is. Up to the time of
writing, the observations have only confirmed the
judgment we expressed above. We will only add that

* Sirius, 1902, x, and 1904, xii (with drawings and photographs). See also
the recent communications of J. Deseilligny (Bulletin de la Soc. Astr. de France,
1906, iii), where the variations of the spots in Flammarion, and to the south of
Archimedes are described, according to observations with a 4-inch Bardou
telescope with a power of 160. The variations are a normal phenomenon, as in
the case of all particularly dark lunar spots ; they are repeated in much the
same form every month, because they depend on the duration and angle of
incidence of the solar radiation.

158 THE MOO]*

the lines and streaks are almost always the least direct
gorges, valleys, depressions, cavities, etc., that are only
gradually; exposed to the sun-light, and bleach more
slowly; and these can be followed in a much finer
form in the much-terraced slopes of Copernicus. We
may , repeat that the recent announcements from
America, which usually command such confidence on
account of the size of the instruments employed, have not
yet made any appreciable contribution to our knowledge
of lunar conditions.; of the monthly variations in the
appearance of the fifrer features. It is very important
to bear well in mindtall that was discovered by German
observers, so that further investigation may build on
this, instead of losing itself along a false path.; The
first epochal works, on the moon came from German
writers, and the greatest map of the moon was con-
structed in Germany. ,

Our study of the nearest and most accessible of
cosmic bodies would hardly be complete if we did not
say a final word on the question of its habitability.
It is not necessary to say much. Even if many of
our measurements of objects on the surface, of our
satellite were incorrect; it remains at le^t, indis-
putable, that it has no atmosphere, in the ordinary
sense, of the word, and no water. Hence we need not
indulge in speculation about living inhabitants. It is
true that gills or tracheae, as well as lungs, serve the
purpose of breathing at the bottom of our aerial
ocean, and that bacilli, for instance, can endure an
intense cold,, comparable • to that of space without
perishing. Iji this way . we might grant that living
things of unknown organisation might subsist on
our satellite. But the only question of great interest
for us is whether beings approaching the human type
could live there.

Sometimes we find imaginative writers seeing
traces of ' vegetation ' in the moon's colour-changes.

Fig. 66. The authors observatory at Landstuhl, with 65-inch and 7- inch
refir.ct ^rs, at an elevation of 450 feet.

160 THE MOON

But vegetation gives off oxygen during the day-time
and carbonic acid at night, and so lives in ' air.' It
is, , therefore, unmeaning to speak of inhabitants or
organisms of any kind intelligible to us on a planetary
waste without air or water. The largest telescopes in
the world and the most laborious research cannot yield
this result. But work that yields us a more accurate
knowledge of those localities that are found to be most
effective in bringing us nearer the solution of the moon's
hieroglyphics, is sure to lead to general cosmic as well
as specifically lunar results. How much material may
be gathered in such research by either professional or
amateur astronomer may be judged from the small maps
given in the present work and the perspective opened
out on page 20.

We come back therefore, to the starting point of
our work. The cuneiform writings on the moon's sur-
face are destined to give us fresh and clearer ideas as to
the natural development of our solar system, provided
our astronomers understand the signs of the times and
do not let the opportunities be lost.

*oo

.- kju^

UNIVERSITY OF CALIFORNIA LIBRAS.'
BERKELEY

tARY

<Q4

Return to desk from which borrowed.
This book is DUE on the last date stamped below.

FEB^fo
OCT 16 1959

LD 21-lQ0m-ll,'A9 (B714Gfll6)47G

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "The Moon in Modern Astronomy: Summary of Twenty Years Selenographic Work ..."

See other formats